Updated version from 0.1.2 to 1.0.1 in VERSION, README.md etc.

The recent `1.0.0` tag left these set to `0.1.2`.
I've correct it for the next version in `ThumborRails::VERSION`, and changed the `README.md` to suggest `~> 1.0`.
I also updated `Gemfile.lock`, but I'd suggest that be deleted and added to `.gitignore`.