diff --git a/.rubocop-2.1.yml b/.rubocop-2.1.yml
index 1152a0cb..f182c198 100644
--- a/.rubocop-2.1.yml
+++ b/.rubocop-2.1.yml
@@ -12,3 +12,14 @@ Layout/IndentHeredoc:
 
 Style/HashSyntax:
   Enabled: false
+
+Naming/UncommunicativeMethodParamName:
+  Enabled: false
+
+Lint/HandleExceptions:
+  Enabled: false
+
+Metrics/LineLength:
+  Exclude:
+    - 'test/resolver/native_test.rb'
+  Max: 140
diff --git a/.rubocop-2.3.yml b/.rubocop-2.3.yml
index 7947689b..586aed12 100644
--- a/.rubocop-2.3.yml
+++ b/.rubocop-2.3.yml
@@ -1,7 +1,18 @@
 inherit_from: .rubocop.yml
 
+require: rubocop-performance
+
 # TODO: remove this if min supported version of ruby is 2.3
 Style/HashSyntax:
   Enabled: false
 
+Naming/MethodParameterName:
+  Enabled: false
 
+Lint/SuppressedException:
+  Enabled: false
+
+Layout/LineLength:
+  Exclude:
+    - 'test/resolver/native_test.rb'
+  Max: 140
diff --git a/.rubocop.yml b/.rubocop.yml
index 8fe88c5e..613e314d 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -17,11 +17,6 @@ AllCops:
     - 'www/**/*'
     - 'lib/httpx/extensions.rb'
 
-Metrics/LineLength:
-  Exclude:
-    - 'test/resolver/native_test.rb'
-  Max: 140
-
 Metrics/MethodLength:
   Max: 200
 
@@ -36,9 +31,6 @@ Naming/FileName:
 Layout/EndAlignment:
   EnforcedStyleAlignWith: variable
 
-Lint/HandleExceptions:
-  Enabled: false
-
 Lint/RescueException:
   Exclude:
     # starts the server in a new thread
diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index 5525fb4d..e2b15642 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -40,5 +40,3 @@ Style/Documentation:
 Naming/AccessorMethodName:
   Enabled: false
 
-Naming/UncommunicativeMethodParamName:
-  Enabled: false
diff --git a/Gemfile b/Gemfile
index 932aab84..edfc3700 100644
--- a/Gemfile
+++ b/Gemfile
@@ -13,7 +13,8 @@ if RUBY_VERSION < "2.2"
   gem "net-ssh", "~> 4.2.0", require: false
   gem "rb-inotify", "~> 0.9.10", require: false
 else
-  gem "rubocop", "~> 0.61.1", require: false
+  gem "rubocop", "~> 0.78.0", require: false
+  gem "rubocop-performance", "~> 1.5.2", require: false
 end
 
 platform :mri do
diff --git a/lib/httpx/adapters/faraday.rb b/lib/httpx/adapters/faraday.rb
index aac3b905..8a2e480a 100644
--- a/lib/httpx/adapters/faraday.rb
+++ b/lib/httpx/adapters/faraday.rb
@@ -195,16 +195,16 @@ module Faraday
           response_headers.merge!(response.headers)
         end
         @app.call(env)
-      rescue OpenSSL::SSL::SSLError => err
-        raise SSL_ERROR, err
+      rescue OpenSSL::SSL::SSLError => e
+        raise SSL_ERROR, e
       rescue Errno::ECONNABORTED,
              Errno::ECONNREFUSED,
              Errno::ECONNRESET,
              Errno::EHOSTUNREACH,
              Errno::EINVAL,
              Errno::ENETUNREACH,
-             Errno::EPIPE => err
-        raise CONNECTION_FAILED_ERROR, err
+             Errno::EPIPE => e
+        raise CONNECTION_FAILED_ERROR, e
       end
 
       private
diff --git a/lib/httpx/plugins/digest_authentication.rb b/lib/httpx/plugins/digest_authentication.rb
index b5b075e9..42eff469 100644
--- a/lib/httpx/plugins/digest_authentication.rb
+++ b/lib/httpx/plugins/digest_authentication.rb
@@ -107,7 +107,7 @@ module HTTPX
 
           if qop || sess
             cnonce = make_cnonce
-            nc = format("%08x", nc)
+            nc = format("%<nonce>08x", nonce: nc)
           end
 
           a1 = if sess
diff --git a/lib/httpx/plugins/proxy/socks5.rb b/lib/httpx/plugins/proxy/socks5.rb
index b3ed3992..61434753 100644
--- a/lib/httpx/plugins/proxy/socks5.rb
+++ b/lib/httpx/plugins/proxy/socks5.rb
@@ -77,7 +77,7 @@ module HTTPX
               case method
               when PASSWD
                 transition(:authenticating)
-                return
+                nil
               when NONE
                 __on_socks5_error("no supported authorization methods")
               else
diff --git a/lib/httpx/pool.rb b/lib/httpx/pool.rb
index bf8c424a..b2435eea 100644
--- a/lib/httpx/pool.rb
+++ b/lib/httpx/pool.rb
@@ -33,9 +33,9 @@ module HTTPX
         end
         @timers.fire
       end
-    rescue StandardError => ex
+    rescue StandardError => e
       @connections.each do |connection|
-        connection.emit(:error, ex)
+        connection.emit(:error, e)
       end
     end
 
diff --git a/lib/httpx/resolver/https.rb b/lib/httpx/resolver/https.rb
index b5f1afd9..8c197206 100644
--- a/lib/httpx/resolver/https.rb
+++ b/lib/httpx/resolver/https.rb
@@ -94,11 +94,11 @@ module HTTPX
 
     def on_response(request, response)
       response.raise_for_status
-    rescue Error => ex
+    rescue Error => e
       connection = @requests[request]
       hostname = @queries.key(connection)
-      error = ResolveError.new("Can't resolve #{hostname}: #{ex.message}")
-      error.set_backtrace(ex.backtrace)
+      error = ResolveError.new("Can't resolve #{hostname}: #{e.message}")
+      error.set_backtrace(e.backtrace)
       emit(:error, connection, error)
     else
       parse(response)
diff --git a/test/support/minitest_extensions.rb b/test/support/minitest_extensions.rb
index da9e3bef..fefffd4d 100644
--- a/test/support/minitest_extensions.rb
+++ b/test/support/minitest_extensions.rb
@@ -24,7 +24,7 @@ module MinitestExtensions
   module FirstFailedTestInThread
     def self.prepended(*)
       super
-      HTTPX::Session.__send__(:include, SessionExtensions)
+      HTTPX::Session.include SessionExtensions
     end
 
     def setup
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 39da0dbf..f54fd104 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -14,8 +14,8 @@ end
 
 require "httpx"
 
-Dir[File.join(".", "test", "support", "*.rb")].each { |f| require f }
-Dir[File.join(".", "test", "support", "**", "*.rb")].each { |f| require f }
+Dir[File.join(".", "test", "support", "*.rb")].sort.each { |f| require f }
+Dir[File.join(".", "test", "support", "**", "*.rb")].sort.each { |f| require f }
 
 # Ruby 2.3 openssl configuration somehow ignores SSL_CERT_FILE env var.
 # This adds it manually.