Take dependencies only on fog-aws and fog-google

[andyvanosdale]

The fog project has become enormous with all the dependencies it now pulls in from every provider it supports. asset_sync only needs the AWS and Google dependencies.

Instead of pulling in all of fog, the gemspec should be explicit and specify only fog-aws and fog-google. Ideally, it doesn't have a dependency on either (as not everyone needs both) and there is a more plug-in architecture that allows asset_sync consumers to pull in only what they need.

[PikachuEXE]

2.0.0 released
Have a try!