Upgrade newrelic gem

* Specified version gives alert that newrelic "requires a security update for
  their Postgres explain plan support"
* Gem version was last set in July 2013: https://github.com/thoughtbot/suspenders/commit/8f133d2bd0f67097495a9c120f724754ef7b0285#diff-2b85b2e387999d51ca372ef132583e80

![screen shot 2014-11-06 at 12 23 41 pm](https://cloud.githubusercontent.com/assets/601515/4943258/d2df995c-65f2-11e4-86d9-8a20821c1ae0.png)