Make brew ruby exit with the status of the executed command.

Library/Homebrew/dev-cmd/ruby.rb

@@ -23,9 +23,13 @@ module Homebrew
   def ruby
     ruby_args.parse
 
+    begin
       safe_system ENV["HOMEBREW_RUBY_PATH"],
                   "-I", $LOAD_PATH.join(File::PATH_SEPARATOR),
                   "-rglobal", "-rdev-cmd/irb",
                   *ARGV
+    rescue ErrorDuringExecution => e
+      exit e.status.exitstatus
+    end
   end
 end