Bundle: make xcodeproj faster on mac

Gemfile

@@ -35,6 +35,11 @@ group :development do
   # Explicitly add this, otherwise it might sometimes be missing:
   # https://github.com/lemurheavy/coveralls-ruby/blob/master/coveralls-ruby.gemspec#L23.
   gem 'simplecov'
+
+  if RUBY_PLATFORM.include?('darwin')
+    # Make Xcodeproj faster
+    gem 'libxml-ruby'
+  end
 end
 
 group :debugging do

Gemfile.lock

@@ -114,6 +114,7 @@ GEM
     kicker (3.0.0)
       listen (~> 1.3.0)
       notify (~> 0.5.2)
+    libxml-ruby (2.7.0)
     listen (1.3.1)
       rb-fsevent (>= 0.9.3)
       rb-inotify (>= 0.9)
@@ -185,6 +186,7 @@ DEPENDENCIES
   github-markup
   i18n (= 0.6.4)
   kicker
+  libxml-ruby
   mime-types (< 2)
   mocha (~> 1.0.0)
   mocha-on-bacon