Update CI workflow

.github/workflows/maven.yml

@@ -17,13 +17,13 @@ jobs:
     # Run steps
     steps:
     # Pull changes
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v2.3.4
     # Cache artifacts - however this has the downside that we don't get notified of
     # artifact resolution failures like invalid repository
     # Nevertheless the repositories should be more stable and it makes no sense to pull
     # a same version every time
     # A dry run would make more sense
-    - uses: actions/cache@v1
+    - uses: actions/cache@v2.1.3
       with:
         path: ~/.m2/repository
         key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
@@ -31,7 +31,7 @@ jobs:
           ${{ runner.os }}-maven-
     # Setup Java
     - name: Set up JDK
-      uses: actions/setup-java@v1.3.0
+      uses: actions/setup-java@v1.4.3
       with:
         # Use Java 8, because it's minimum required version
         java-version: 8