Mention Lua version change in changelog
## Changelog
+### 1.2.1
+
+Release pending.
+
+- Upgrade included Lua version to new bug-fix release 5.3.6. See
+ the upstream documentation https://www.lua.org/bugs.html#5.3.5
+ for the bugs which have been fixed.
+
### 1.2.0
Released 2020-08-15
