Much slower than standard compass command

Hi!

I tried to use gulp-compass, but it is so much slower than invoking `compass compile` or `compass watch`. Regular `compass compile` takes no more than 0.5 sec to compile all the files, with `gulp-compass` it takes even few seconds.

My task:

```
gulp.task('compass', function() {
return gulp.src(SASS_FILES_PATTERN)
.pipe(compass({
config_file: path.join(ROOT_PATH, 'config.rb'),
css: 'css',
sass: 'sass',
project: ROOT_PATH,
}));
});
```

What could be wrong with this configuration?

Start with the gulp task in the issue, including SASS_FILES_PATTERN, config.rb, and the compass() options, then compare its behavior with the referenced `compass compile` and `compass watch` commands. Done means identifying the configuration or plugin behavior responsible for the slower compilation and documenting a reproducible comparison.

Written by the indexing model from the issue text.