Upgrade to RSpec 3

* `should` syntax has been deprecated in favor of the newer `expect` syntax. The
specs were updated to use `expect`.
* `treat_symbols_as_metadata_keys_with_true_values` is now the default behavior in
RSpec 3 and is no longer a configuration option.
* Unused `factories.rb` file was removed
Merge pull request #23 from JoelQ/jq-rspec-3

Upgrade to RSpec 3