fix: remove unnecessary comments from video.min.js

This involves updating to latest version of uglify and setting
"screwIE8" to false since that is a default in 2.7. However, this makes
"preserveComments" "some" work as it is supposed to work.

Fixes #3707

build/grunt.js

@@ -128,6 +128,7 @@ module.exports = function(grunt) {
         sourceMapIn: 'build/temp/video.js.map',
         sourceMapRoot: '../../src/js',
         preserveComments: 'some',
+        screwIE8: false,
         mangle: true,
         compress: {
           sequences: true,

package.json

@@ -59,7 +59,7 @@
     "grunt-contrib-cssmin": "~0.6.0",
     "grunt-contrib-jshint": "~0.11.3",
     "grunt-contrib-less": "~0.6.4",
-    "grunt-contrib-uglify": "~0.11.0",
+    "grunt-contrib-uglify": "^2.0.0",
     "grunt-contrib-watch": "~0.1.4",
     "grunt-coveralls": "^1.0.0",
     "grunt-exorcise": "^1.0.1",