chore: add ansi reset code, rather than wrapping in white

lib/pact/provider/matchers/messages.rb

@@ -36,9 +36,9 @@ def expected_desc_for_it expected
       def colorize_if_enabled formatted_diff, color_enabled
         if color_enabled
           # RSpec wraps each line in the failure message with failure_color, turning it red.
-          # To ensure the lines in the diff that should be white, stay white, wrap each line
-          # in ANSI white.
-          formatted_diff.split("\n").collect{ |line| Rainbow(line).white }.join("\n")
+          # To ensure the lines in the diff that should be white, stay white, put an
+          # ANSI reset at the start of each line.
+          formatted_diff.split("\n").collect{ |line|"\e[0m#{line}" }.join("\n")
         else
           formatted_diff
         end

spec/lib/pact/provider/matchers/messages_spec.rb

@@ -12,7 +12,8 @@ module Matchers
         let(:diff_formatter) { Pact::Matchers::UnixDiffFormatter }
         let(:message) { "line1\nline2"}
         let(:output_message) { "Actual: actual\n\n#{message}"}
-        let(:output_message_with_resets) { "Actual: \e[37mactual\e[0m\n\n#{Rainbow('line1').white}\n#{Rainbow('line2').white}"}
+        let(:r) { "\e[0m" }
+        let(:output_message_with_resets) { "Actual: \e[37mactual\e[0m\n\n#{r}line1\n#{r}line2"}
         let(:diff) { double("diff") }
         let(:actual) { "actual" }
         let(:color_enabled) { true }