Use FileSystem change event to trigger uploads

[jasonsanjose]

See jasonsanjose/brackets-sass#20.

The brackets-sass plugin uses node to compile a .css file. This only fires a FileSystem change event http://brackets.io/docs/current/modules/filesystem/FileSystem.html and not a documentSaved event as used here https://github.com/theproducer/brackets-ftp/blob/master/main.js#L453.

Making this change should allow for your extension to capture other external file changes that Brackets doesn't capture (e.g. images, directories, etc.)