chore: RuboCop lint Style/Globalvars (#943)

.rubocop_todo.yml

@@ -48,12 +48,6 @@ Style/Documentation:
     - 'lib/faraday/response/raise_error.rb'
     - 'lib/faraday/utils.rb'
 
-# Offense count: 2
-# Configuration parameters: AllowedVariables.
-Style/GlobalVars:
-  Exclude:
-    - 'script/generate_certs'
-
 # Offense count: 1
 Style/MultipleComparison:
   Exclude:

script/generate_certs

@@ -1,14 +1,14 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
-# Usage: generate_certs
+# Usage: generate_certs [options]
+#   options:
+#     -s     Display shell exports that link env variables to filenames
 # Generate test certs for testing Faraday with SSL
 
 require 'openssl'
 require 'fileutils'
 
-$shell = ARGV.include? '-s'
-
 # Adapted from WEBrick::Utils. Skips cert extensions so it
 # can be used as a CA bundle
 def create_self_signed_cert(bits, cname, _comment)
@@ -29,7 +29,7 @@ end
 def write(file, contents, env_var)
   FileUtils.mkdir_p(File.dirname(file))
   File.open(file, 'w') { |f| f.puts(contents) }
-  puts %(export #{env_var}="#{file}") if $shell
+  puts %(export #{env_var}="#{file}") if ARGV.include? '-s'
 end
 
 # One cert / CA for ease of testing when ignoring verification