e.g. `ActiveRecord::Migration[5.1]`
Fixes#949
Following the example of the devise gem, use erb. In addition, add
the `.erb` file extension to fix syntax highlighting in editor.
Deletes create_versions_spec.rb because the file is no longer valid
ruby so those tests will have to be re-written. We can either
generate a valid ruby file and continue to use similar assertions,
or we can convert those features to use erb, which will have the
benefit of cleaner generated files.
Jared Beck