update fast-lane link in contributing.md
The developer guide is for anyone wanting to contribute directly to the Checkov project.
-If you've already developed new checks we'd be happy to take a look at them and merge them as part of the [fast-lane](Fast-lane for new checks).
+If you've already developed new checks we'd be happy to take a look at them and merge them as part of the [fast-lane](https://github.com/bridgecrewio/checkov/issues?q=is%3Aopen+is%3Aissue+label%3Afast-lane).
