Skip sourcemap files matched in files list since they already get rev-ed based on the compiled file

[travi]

Since this plugin already has the behavior of automatically revving a sourcemap file to match the compiled file, processing the original sourcemap as well causes odd behavior. One example of this odd behavior includes ENOENT errors when revving in place since the filename changes before processing the match (Warning: ENOENT, no such file or directory 'c:\app.css.map').

Since this behavior is not obvious, I think it would be valuable if the plugin took its automatic behavior into account when processing the file list so that matched sourcemap files were simply skipped.