Under tmux hangs if dialog must be displayed

[hwine]

I tried to upgrade "Calendar 2", which has a menu bar presence. When you try to update from the App Store, a dialog will pop up saying it can not be updated while running.

When running the equivalent command using mas from a tmux window running in iTerm, mas just hangs. (I have reattach-to-user-namespace configured.)

When I run the same command in a plain iTerm window, the dialog will appear.

[chris-araman]

Likely related to #128 and #89.