chore: specify correct default branch in CONTRIBUTION.md (apify#1771)

There is an incorrect branch specified in the guidelines: instead of
`master`, there is `main` branch mentioned, which does not exist.

Author: JMatej

CONTRIBUTING.md

@@ -247,7 +247,7 @@ Add languages by adding new folders at the appropriate path level.
 
 1. Make your changes following the guidelines above
 2. Test locally using provided npm commands
-3. Submit a pull request to the `main` branch
+3. Submit a pull request to the `master` branch
 4. Ensure all CI checks pass
 
 ## Development workflow