Gemfile in stripe-4.18.0 vs Gemfile in stripe-4.18.1

@@ -16,10 +16,12 @@
   # Rubocop changes pretty quickly: new cops get added and old cops change
   # names or go into new namespaces. This is a library and we don't have
   # `Gemfile.lock` checked in, so to prevent good builds from suddenly going
   # bad, pin to a specific version number here. Try to keep this relatively
   # up-to-date, but it's not the end of the world if it's not.
-  gem "rubocop", "0.50.0"
+  # Note that 0.57.2 is the most recent version we can use until we drop
+  # support for Ruby 2.1.
+  gem "rubocop", "0.57.2"
 
   # Rack 2.0+ requires Ruby >= 2.2.2 which is problematic for the test suite on
   # older Ruby versions. Check Ruby the version here and put a maximum
   # constraint on Rack if necessary.
   if RUBY_VERSION >= "2.2.2"