📝 update CONTRIBUTORS.md

Author: builtinnya

CONTRIBUTORS.md

@@ -4,6 +4,8 @@
   - [Housekeeping: Pipenv & Slimmer package by Ketouem · Pull Request #6 · builtinnya/aws-sns-slack-terraform](https://github.com/builtinnya/aws-sns-slack-terraform/pull/6)
 - [davearata](https://github.com/davearata)
   - [Codepipeline slack message support](https://github.com/builtinnya/aws-sns-slack-terraform/pull/4)
+- [Jonathan](https://github.com/allcloud-jonathan)
+  - [Username Prefix && housekeeping by allcloud-jonathan · Pull Request #9 · $builtinnya/aws-sns-slack-terraform](https://github.com/builtinnya/aws-sns-slack-terraform/pull/9)
 - [Katsutoshi Murakami](https://github.com/umisora)
   - [Default emoji support](https://github.com/builtinnya/aws-sns-slack-terraform/pull/2)
 - [Mehdi Ben Abdallah](https://github.com/mbenabda)