update gruntfile.js to let jshint adhere to .jshintrc

currently the `jshint:all` task doesn't take the .jshintrc-file into account. This pull corrects that.
Merge pull request #203 from gebrits/patch-1

update gruntfile.js to let jshint adhere to .jshintrc
Merge branch 'master' of https://github.com/linnovate/mean