Hugo 0.84.1: A couple of Bug Fixes

This is a bug-fix release with a couple of important fixes.

• Fix language menu config regression 093dacab @bep #8672
• config: Fix merge of config with map[string]string values. 4a9d408f @bep #8679
• markup: Rename Header(s) to Heading(s) in ToC struct a7e3da24 @bep