Fix considering extended directory using .bowerrc

Hi there, 

i try to use ```bower.commans.list({paths: true})``` into the ```grunt-bower-task``` module.
also i extended directory path using ```.bowerrc```. then, this canonicalDir is not considered a extented directory.
so I fixed that. i thinks related to this isseu. https://github.com/bower/bower/issues/714

thank you.