EXCEPT DISTINCT parsed to EXCEPT ALL

[JordyHeusdensDT]

The latest ZetaSQL (2021.09.1) doesn't handle EXCEPT DISTINCT properly.

Assume we have some Query 'Q1' (as String) that contains EXCEPT DISTINCT.
We parse Q1 via ZetaSQL and format it again to get a String again. This String is a new Query 'Q2'

Expected resulted: Both Q1 and Q2 have EXCEPT DISTINCT.
Current result: Q1 has EXCEPT DISTINCT, Q2 has EXCEPT ALL.

See #82 for fix.