Add Fedora 20 support

The internal bits of the module works fine on Fedora 20, but it was not running as F20 was not explicitly allowed.  This patch changes that.

F20 is the only platform I tested on.  I believe it reasonable to expect versions prior to F20 work, but I have not tested.  I'm unaware of any planned changes in future versions of F20.  Given that, I'm inclined to to remove the 'case $::operatingsystemmajrelease' check.  But I don't know which would be more surprising to the end user: having it fail to work on a newer/older version because the code is wrong; or, not having it work because the OS version is not explicitly set in the module.  Considering how I discoved the failing, I would answer the former, but the conservative sysadmin in me followed the existing idiom and implemented only the latter.

I'll be more than happy to implement a non-checking version; just share your thoughts/preferences.