Fix slack link for contributing (#1059)

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 Thank you for considering contributing to tfsec! 
 
-We've documented the process of adding a new check below. If you have any other specific questions/problems that are preventing you from raising a PR, please get in touch with us! You can [find us on Slack](https://join.slack.com/t/tfsec/shared_invite/zt-i0vo9rp2-tEizIaT1dS4Eu2hVIsvwDg) - or simply [raise an issue](https://github.com/aquasecurity/tfsec/issues/new) and we'll do our best to help you out.
+We've documented the process of adding a new check below. If you have any other specific questions/problems that are preventing you from raising a PR, please get in touch with us! You can [find us on Slack](https://join.slack.com/t/tfsec/shared_invite/zt-o6c7mgoj-eJ1sLDv595sKiP5OPoHJww) - or simply [raise an issue](https://github.com/aquasecurity/tfsec/issues/new) and we'll do our best to help you out.
 
 ## Adding a New Check
 
@@ -139,4 +139,4 @@ make pr-ready
 
 This will run all of the tests, validate for cyclomatic complexity, spelling mistakes and run the end to end tests in the `./example` folder.
 
-Raise your PR when this passes okay (you can expect to see failures from the example run, but overall `make pr-ready` should exit 0)
+Raise your PR when this passes okay (you can expect to see failures from the example run, but overall `make pr-ready` should exit 0)