Update actions/checkout action to v2

Author: renovate-bot

.github/workflows/java.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2
     - name: Set up JDK 1.8
       uses: actions/setup-java@master
       with: