Remove file.clone() so that upstream file decorations are not lost

For example, when `gulp-bytediff` is used to see the savings from gzip,
it attaches a "start value" to the file and looks for it later to calc
the savings. By calling file.clone(), this annotation is lost.
And make tests pass!
Merge pull request #5 from ngConsulti/pull-request/dont-clone-file

Remove file.clone() so that upstream file decorations are not lost