Fix id names in rst renders after docutils 0.18

Fix id names changing in rst renders with the upgrade to docutils 0.18
by enforcing the old default value `id` for `auto_id_prefix`.

See: https://docutils.sourceforge.io/RELEASE-NOTES.html#release-0-18-2021-10-26

co-authored-by: Tyler Dixon <tylerdixon@github.com>

Author: pudiva

lib/github/commands/rest2html

@@ -160,6 +160,7 @@ SETTINGS = {
     'syntax_highlight': 'none',
     'math_output': 'latex',
     'field_name_limit': 50,
+    'auto_id_prefix': 'id',
 }
 
 default_highlight_language = None