Catch ValueError when choosing iOS version target
Catch ValueError when choosing iOS version target

When the user reaches the following point, if they enter (for example) `8.1`, rather than `1`, `python` throws a `ValueError`, because it's trying to convert to an `int`. This moves the version selection code inside the `"Invalid selection"` `try: except:` block, which gives the user another chance to enter the correct value, rather than crashing.

    Available iOS versions:
      [1] iOS 8.1
      [2] iOS 7.1
      [3] iOS 10.2
      [4] iOS 8.2
    Which iOS version do you want to target: 4
pybee/briefcase