title: SourceTree click ' terminal button' to switch terminal not work
body: <p>Mac : sierra 10.12.5
  sourceTree: 2.6(123)
  iTerm2: Build 3.0.15</p>
  
  <p>when i use the top right button "terminal"(near Setting) to switch to my iTerm2. it crashed!
  no matter i update to 2.6, it doesn't work!</p>
  
  <p><a href="https://i.stack.imgur.com/vrQlN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vrQlN.png" alt="enter image description here"></a></p>