Use Java 15 in CI

Author: fpoli

.github/workflows/test.yml

@@ -30,6 +30,11 @@ jobs:
         run: rustup self update # Windows needs to update rustup
         continue-on-error: true # MacOS doesn't allow to update rustup
 
+      - name: Set up Java
+        uses: actions/setup-java@v1
+        with:
+          java-version: '15'
+  
       - name: Install NPM dependencies
         run: npm install