Merge pull request #28 from saeg/github-actions-ubuntu-20.04

Update GitHub Actions build to use Linux Ubuntu 20.04 (ubuntu-20.04)

Author: andrioli

.github/workflows/main.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-18.04, windows-2019]
+        os: [ubuntu-20.04, windows-2019]
         java: [6, 7, 7.0.121, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
     runs-on: ${{ matrix.os }}
     steps: