title: Tower Won't Roll Back Commit
body: <p>I am trying to roll back to a particular commit using Tower v 1.4.16 with Mac 0SX v 10.6.8. When I right-click on the commit, the option to "Roll Back to This Commit" is greyed out. Why is this happening?</p>
  
  <p><img src="https://i.stack.imgur.com/TLmh2.png" alt="enter image description here"></p>