Update CI.yml

Author: maximiliani

.github/workflows/CI.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        jdk: [ 13, 17, 18 ]
+        jdk: [ 17 ]
     steps:
       - name: Checkout repo
         uses: actions/checkout@v2