Generate safe sourcemaps
Generate safe sourcemaps

The previous comment syntax was unsafe with Internet Explorer. This
change copies the equivalent upstream change to use the more robust
nested comment:

```javascript
/*
//@ sourceMappingURL=file.min.js.map
*/
```

See:
    https://github.com/mishoo/UglifyJS2/issues/108
    http://bugs.jquery.com/ticket/13274

denisbabineau/grunt-contrib-uglify,gruntjs/grunt-contrib-uglify,MoLow/grunt-contrib-uglify,okonomiyaki3000/grunt-contrib-uglify,tempbottle/grunt-contrib-uglify,cvibhagool/grunt-contrib-uglify,reppners/grunt-contrib-uglify,UltCombo/grunt-contrib-uglify,MarianVasile/grunt-contrib-uglify,devgrok/grunt-contrib-uglify