add sass-cache: false argument

``` javascript
gulp.task('compass', function(cb) {
return gulp.src(paths.sass)
.pipe(compass({
sass: 'dev/sass',
css: 'build/source',
image: 'img',
cache: false // in order to disable caching, optional
}))
})
```

Start by locating the gulp-compass entry point that forwards the options shown in the issue, and inspect how caching is currently configured. Confirm the expected Sass cache option and verify that the example can disable caching without affecting the other Compass settings.

Written by the indexing model from the issue text.