Do not automatically update

[Haarolean]

I find it irritating that once I deploy something, flyctl updates itself and it blocks my work. I want to do my job without this thing getting in my path. Alternatives:

1. make it skippable, like brew itself updates sometimes but if you hit ctrl+c you can skip it
2. implement a configuration property to reduce these annoyances
3. do this in the background and let me execute my commands

$ fly deploy         
Automatically updating 0.3.55 -> 0.3.64.
Running automatic upgrade [brew upgrade flyctl]