fix the file filtering rule of '!**/*.(scss,sass,css)'

[yanCode]

in task copy:app, it's supposedly to filter out files of styles, such as scss, sass & css. However, according to http://gruntjs.com/configuring-tasks#globbing-patterns

This syntax using '()' is incorrect, instead, {} should be used, e.g., '!*/.{scss,sass,css}' as in my fix.