Use the same version of ActiveRecord as transition

- This forces a `mysql2` gem upgrade too, as running the tests doesn't
  work with 0.3.11. The `mysql2` gem is also now the same as transition.
Merge pull request #88 from alphagov/use_same_activerecord_version_as_transition

Use the same version of ActiveRecord as transition
Use ' instead of " around the mr-sparkle gem for consistency
Merge pull request #89 from alphagov/single_quotes_in_gemfile

Use ' instead of " around the mr-sparkle gem for consistency