copy subtask to support multiple destinations

[maxwellpeterson-wf]

@travissanderson-wf requested support to copy to multiple destinations:

gulp.task('dartLib', wGulp.getDeps('dartLib'), wGulp.copy({
    changed: true,
    src: ['src/wTransport.dart', 'dist/wTransportGlobal.bundle.js'],
    dest: ['lib/', 'examples/dart/web/']
}));

First thoughts on implementation:
I think gulp recently released support for this with a syntax like so:

gulp.src('file.ext')
    .dest('locationA')
    .dest('locationB')

If that is indeed the case, the copy subtask should be able to apply .dest() chains in a loop.

[travissanderson-wf]

@markerickson-wf fyi