fixed #721

Spiderable failed when facebook bot tried to fetch without parametres eg. `http://meteorrain.meteor.com` - Spiderable now depending on the reg.ex to catch the bot user agent.

The reg.ex failed to catch this due to a change in facebook bot header. Header going from low case to CamelCase like the `LinkedInBot`

* Fixed by making the user agent string lower case
* Added linkedin bot

*Tested in facebook and linkedin*