travis: forbid rainbow 2.2.1 as it has an installation bug (ku1ik/rainbow#44)

toy · toy · commit 01411bd0c505 · 2017-03-21T00:45:31.000+01:00
diff --git a/.rubocop.yml b/.rubocop.yml
@@ -3,6 +3,9 @@ AllCops:
     - '*.gemspec'
     - 'vendor/**/*'
 
+Bundler/OrderedGems:
+  Enabled: false
+
 Lint/EndAlignment:
   EnforcedStyleAlignWith: variable
 
diff --git a/Gemfile b/Gemfile
@@ -12,4 +12,5 @@ end
 
 if RUBY_VERSION >= '2.0'
   gem 'travis_check_rubies', '~> 0.2'
+  gem 'rainbow', '!= 2.2.1' # TODO: remove when sickill/rainbow#44 is resolved
 end
