Use Java 16 when deploying javadocs (#2028)

.github/workflows/javadocs.yml

@@ -16,6 +16,11 @@ jobs:
       - name: Checkout 🛎️
         uses: actions/checkout@v2.3.1
 
+      - name: Set up JDK 1.16 🍵
+        uses: actions/setup-java@v2
+        with:
+          distribution: 'adopt'
+          java-version: '16'
       - name: Build Javadocs 🔧 
         run: |
           cd Plan
@@ -31,8 +36,9 @@ jobs:
           cp scripts/index.html javadocs/index.html
           cd javadocs
           touch .nojekyll
+
       - name: Deploy 🚀
-        uses: JamesIves/github-pages-deploy-action@4.0.0
+        uses: JamesIves/github-pages-deploy-action@4.1.4
         with:
           branch: gh-pages # The branch the action should deploy to.
           folder: javadocs # The folder the action should deploy.