Add .dev TLD to allowed gTLDs

Hi everyone, 

this PR is more of a question than a PR. I'm using this library in Rails and access my app under `http://my_app.dev/` with the `.dev` toplevel domain. Doing so results in `twitter-text-rb` not recognizing text as a URL and thus e.g. counting the tweet length "incorrectly". How would you handle such a case, do you have a suggestions for locally whitelisting `.dev` domains?

Thanks in advance!

Best,
Thomas