Update maven.yml to use "latest" OS runners (#437)

Author: chrjohn

.github/workflows/maven.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-18.04, macOS-latest, windows-2016]
+        os: [ubuntu-latest, macOS-latest, windows-latest]
         java: [8, 11, 17]
       fail-fast: false
       max-parallel: 4