introduced async / updated dependencies and devDependencies

grunt.util.async is deprecated. See
http://gruntjs.com/api/grunt.util#grunt.util.async for details.
stopped using deprecated utilities

grunt.util._ and grunt.util.async are deprecated. See
http://gruntjs.com/api/grunt.util#external-libraries for details.
Merge pull request #3 from shinnn/master

Update dependencies / Remove deprecated utilities