Empty .bowerrc files should not throw an error.

Bower throws an error whenever it sees an empty `.bowerrc` file.

As much as empty JSON code is invalid, but I have a tendency to create empty `.bowerrc` files in my projects, and *then* call `bower init`. As a result, `bower init` just drops dead and throws an error. Very annoying for me.

I'm not sure if this is annoying for other people. I'll just leave this here for you guys to take into consideration.