Prevent Frozen String mutation

Author: JonRowe

lib/rspec/core/option_parser.rb

@@ -22,8 +22,12 @@ def parse(source=nil)
       begin
         parser(options).parse!(args)
       rescue OptionParser::InvalidOption => e
-        failure = e.message
-        failure << " (defined in #{source})" if source
+        failure =
+          if source
+            "#{e.message} (defined in #{source})"
+          else
+            e.message
+          end
         abort "#{failure}\n\nPlease use --help for a listing of valid options"
       end