do not add our lib twice

Author: grosser

bin/spring

@@ -43,6 +43,7 @@ if defined?(Gem)
   end
 end
 
-$LOAD_PATH.unshift File.expand_path("../../lib", __FILE__)
+lib = File.expand_path("../../lib", __FILE__)
+$LOAD_PATH.unshift lib unless $LOAD_PATH.include?(lib) # enable local development
 require 'spring/client'
 Spring::Client.run(ARGV)