Increase sphinx pin now that 1.2.1 is out

1.2.1 fixes the bug that was in 1.2 - so we should go ahead and update.
Keep the pin at below 1.3 because sphinx breaks things.

Change-Id: I63c6159eb23430a181eb20016b35366c2fbbf9f8
Merge "Increase sphinx pin now that 1.2.1 is out"