Pass filename to uglify-js

I had a problem with Uglifyify that some errors didn't have correct file names visible -- but there still was line, column and position there and it was really hard to find where was the real problem.

I've fixed the problem by passing on `file` as `options.filename` to uglify-js.

However in order for this actually work uglify-js needs pull request mishoo/UglifyJS2#562 accepted.