Build: Downgrade uglify-js to fix tests in IE 9

We can upgrade for Migrate 4.0. It's not worth spending time on figuring
out how to fix IE 9 with new UglifyJS at this point.

The `ie` option had to be renamed to `ie8` as the older version doesn't
support the former. In Migrate 4 we can remove it altogether.

Closes gh-479

Gruntfile.js

@@ -169,8 +169,8 @@ module.exports = function( grunt ) {
 
 						// Support: Android 4.0 only
 						// UglifyJS 3 breaks Android 4.0 if this option is not enabled.
-						// This is in lieu of setting ie for all of mangle, compress, and output
-						ie: true
+						// This is in lieu of setting ie8 for all of mangle, compress, and output
+						ie8: true
 					},
 					banner: "/*! jQuery Migrate v<%= pkg.version %>" +
 						" | (c) <%= pkg.author.name %> | jquery.org/license */",

package.json

@@ -35,7 +35,7 @@
 		"grunt": "1.5.3",
 		"grunt-cli": "1.4.3",
 		"grunt-compare-size": "0.4.2",
-		"grunt-contrib-uglify": "5.0.1",
+		"grunt-contrib-uglify": "4.0.1",
 		"grunt-contrib-watch": "1.1.0",
 		"grunt-eslint": "24.0.0",
 		"grunt-karma": "4.0.2",