chore(grunt-contrib-uglify): Updating uglify package to be able to handle `compress: true` and `compress: {}`.
chore(grunt-contrib-uglify): Updating uglify package to be able to handle `compress: true` and `compress: {}`.

Fixes:

[TypeError: Cannot assign to read only property 'warnings' of true]
>> Uglifying source build/videojs.hotkeys.js failed.
Warning: Uglification failed.
Cannot assign to read only property 'warnings' of true.
 Use --force to continue.

ctd1500/videojs-hotkeys,ctd1500/videojs-hotkeys