#61: update ubuntu agents in workflow

Author: vpiotr

.github/workflows/action.yml

@@ -8,7 +8,7 @@ jobs:
 
     strategy:
       matrix:
-        os: [ubuntu-18.04, ubuntu-20.04]
+        os: [ubuntu-latest, ubuntu-20.04]
 
     steps:
       - uses: actions/checkout@v2