comment out global grunt in aliases.js

to avoid jshint error:

    grunt test                                                                                                                              (05-02 14:37)
    Running "newer:jshint" (newer) task
    Running "newer:jshint:all" (newer) task
    Running "jshint:all" (jshint) task
       grunt/aliases.js
          1 |/*global grunt */
                              ^ 'grunt' is defined but never used.
    >> 1 error in 33 files
    Warning: Task "jshint:all" failed. Use --force to continue.
    Aborted due to warnings.