Watching Sass files from `ionic serve`, new in cli v1.1.9

So my changes in scss stoped working after a while and then I noticed when doing ionic serve I was receiving the following error message:

    Starting 'sass'...
[11:46:32] [gulp-sass] no mixin named div-bg-img-with-opacity
Backtrace:
        scss/ionic.app.scss:190 on line 190 in D:/xxx/APP/scss/ionic.app.scss

So I corrected line 190 and everything worked fine again