Update CHANGELOG.md

Author: radeksimko

CHANGELOG.md

@@ -7,6 +7,7 @@ FEATURES:
 ENHANCEMENTS:
 
  - cmd: Introduce version JSON output ([#386](https://github.com/hashicorp/terraform-ls/pull/386))
+ - Utilize CPU better when loading modules ([#391](https://github.com/hashicorp/terraform-ls/pull/391))
 
 ## 0.12.1 (12 January 2021)