Don't fetch the value just to throw it away

Library/Homebrew/cmd/--env.rb

@@ -31,7 +31,7 @@ module Homebrew extend self
       HOMEBREW_SVN HOMEBREW_GIT
       HOMEBREW_SDKROOT HOMEBREW_BUILD_FROM_SOURCE
       MAKE GIT CPP
-      ACLOCAL_PATH PATH CPATH].select{ |key| env.fetch(key) if env.key? key }
+      ACLOCAL_PATH PATH CPATH].select { |key| env.key?(key) }
   end
 
   def dump_build_env env