Include submodules in pull request build action

.github/workflows/pullrequest.yml

@@ -19,6 +19,8 @@ jobs:
         uses: actions/setup-java@v1
         with:
           java-version: 1.8
+      - name: submodules-init
+        uses: snickerbockers/submodules-init@v4
       - name: Build with Maven
         run: mvn -B package
       - name: Archive artifacts