update Gemfile

Author: reshamas

Gemfile

@@ -34,5 +34,5 @@ platforms :mingw, :x64_mingw, :mswin, :jruby do
 end
 
 # Performance-booster for watching directories on Windows
-gem "wdm", "~> 0.1.1", :platforms => [windows]
+gem "wdm", "~> 0.1.1", :platforms => [:windows]