docs: snake_case enums/unions in langref examples

This follows the accepted change to the style guide:
https://github.com/ziglang/zig/issues/2101
7b150dd05eIsaac Freund committed on 10/15/2020, 3:55:57 PM· committed by Veikka Tuominenparent3b4432d
1 file changedLine totals unavailable