Removed travis ci files - no longer needed. Updated Github CI to explicitly run on push and pull requests.

Author: Carlos Matos

.github/workflows/main.yml

@@ -2,7 +2,7 @@ name: OpenScap Workbench CI
 
 # Controls when the action will run. Triggers the workflow on push or pull request
 # events but only for the master branch
-on: push
+on: [push, pull_request]
 
 jobs:
   build-macos: