fix(config): use single-bracket table for commitizen change_type_map

Using [[tool.commitizen.change_type_map]] created a TOML Array of Tables
(AoT), which caused an AttributeError when commitizen tried to call .get()
on it. Changed to [tool.commitizen.change_type_map] so it is parsed as a
plain dict.

Author: zodiacfireworks

pyproject.toml

@@ -184,7 +184,7 @@ version_files = [
   "pyproject.toml:tags/v$version.tar.gz",
 ]
 
-[[tool.commitizen.change_type_map]]
+[tool.commitizen.change_type_map]
 "feat" = "Features"
 "fix" = "Bug Fixes"
 "docs" = "Documentation"