Update CONTRIBUTING.md

Author: CGraczyk

CONTRIBUTING.md

@@ -3,11 +3,7 @@ Contributing to PySCIPOpt
 
 Code contributions are very welcome and should comply to a few rules:
 
-0.  Read [Design principles of PySCIPOpt](#design-principles-of-pyscipopt).
-1.  ## This is currently in transition to the github-actions workflow, integration tests have been setup for linux.
-    - All tests defined in the Continuous Integration setup need to pass:
-    -   [.travis.yml](../../.travis.yml)
-    -   [appveyor.yml](../../appveyor.yml)
+1.  Read [Design principles of PySCIPOpt](#design-principles-of-pyscipopt).
 
 2.  New features should be covered by tests *and* examples. Please
     extend [tests](tests) and [examples](examples). Tests uses pytest