BUGFIX: CL-5741 Fix grunt-grizzly repo url

Till now people without account on github were unable to install
grunt-grizzly package referenced as dependency in package.json.

Fixed url according to npm documentation
(https://www.npmjs.org/doc/files/package.json.html#git-urls-as-dependencies)
Merge pull request #70 from akloboucnik/akl-cl-5741-2

BUGFIX: CL-5741 Fix grunt-grizzly repo url

Reviewed-by: Petr Benes <petr.benes@gooddata.com>