Revert "Bump omniauth-shopify-oauth2"

While trying to install shopify_app to get my changes for [my pull request #40](https://github.com/Shopify/shopify_app/pull/40) working, I got bundler errors saying that omniauth-shopify-oauth2 v1.1.0 wasn't available. I didn't see any v1.1 branch in https://github.com/Shopify/omniauth-shopify-oauth2, nor did I see a "stable" branch in shopify_app, so I created this rollback branch/commit.

Then I merged this branch and my [add-less-rails-bootstrap branch](https://github.com/softcraft-development/shopify_app/tree/add-less-rails-bootstrap) into [no-omniauth-bump-plus-less-rails-bootstrap](https://github.com/softcraft-development/shopify_app/tree/no-omniauth-bump-plus-less-rails-bootstrap). When I used *this* repo/branch, I was able to run the shopify_app generator on a clean Rails 3.2 install without error.

I'm guessing that you're rolling omniauth-shopify-oauth2 forward internally and just haven't pushed the changes yet. If that's the case, then you probably would *not* want to actually merge this PR... and instead make v1.1 available. But as it stands right now, the master branch of shopify_app is broken.