Dummy run that emits 'end' but not saves

After this change `gulp-shell`+`jshint` are compatible with callback way. You see - i dont need to dump "index.js" anywhere. So, full `gulp.dest` is not needed. Here is the example:

```
gulp.task('lint', function(cb) {

  gulp.src("index.js")
      .pipe(shell('jshint <%= file.path %>'))
      .pipe(gulp.dest()) // "end" does not fire if you comment this line
      .once("end", function() {

    console.log("ended!");
    cb();

    // here may be some more code with cb()
    // inside. so cb-way is preferred

  });

});
```