Use Java 14 final release and drop Java 13 build. (assertj#1810)

Author: PascalSchumacher

.github/workflows/cross-version.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        java: [13, 14-ea, 15-ea]
+        java: [14, 15-ea]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2