Revert back to `currentRouteName()` 

As noted in the commit https://github.com/In-Touch/laravel-newrelic/commit/5354361b7fa3c05bb32e4a5b5275bd7669794332 
There was a bug in Laravel 4.1, they added back the method to the Router class
laravel/framework@45ff48321ea625f6997d5d1b13dfec59f0dc08a3
Merge pull request #5 from altrim/patch-2

Revert back to `currentRouteName()`