Gulp postinstall error with imagemin task
Gulp task `imagemin` yields `TypeError: Cannot read property 'on' of defined`, referencing `gulpfile.js:128:6` which calls the `revall` module. 

Changing `"gulp-rev-all"` version to `"^~0.7.6"` in `devdependencies` allowed task to run without error. May be caused by ["Major breaking changes" between v0.7.6 and v0.8.x](https://www.npmjs.com/package/gulp-rev-all#upgrading-to-v0-8-x).
