Fix response not changing with parallel requests

In this order the @env would not be changed by the "on complete"
callbacks, meaning that the response would not change after parallel
requests finish (e.g. JSON would not be parsed).

This would work

  def on_complete(env)
    env[:body].upcase!
  end

But this wouldn't

  def on_complete(env)
    env[:body] = env[:body].upcase
  end

lib/faraday/response.rb

@@ -61,8 +61,8 @@ module Faraday
 
     def finish(env)
       raise "response already finished" if finished?
-      @env = Env.from(env)
       @on_complete_callbacks.each { |callback| callback.call(env) }
+      @env = Env.from(env)
       return self
     end
 

test/env_test.rb

@@ -166,6 +166,14 @@ class ResponseTest < Faraday::TestCase
     end
   end
 
+  def test_body_is_parsed_on_finish
+    response = Faraday::Response.new
+    response.on_complete { |env| env[:body] = env[:body].upcase }
+    response.finish(@env)
+
+    assert_equal "YIKES", response.body
+  end
+
   def test_not_success
     assert !@response.success?
   end