ci: add JDK 15 to build matrix (#210)

Author: sullis

.github/workflows/build.yml

@@ -30,7 +30,7 @@ jobs:
       max-parallel: 4
       matrix:
         # test against latest update of each major Java version, as well as specific updates of LTS versions:
-        java: [8, 8.0.192, 11.0.x, 11.0.3, 12, 13 ]
+        java: [8, 8.0.192, 11.0.x, 11.0.3, 12, 13, 15 ]
     name: Java ${{ matrix.java }}
     env:
       OS: ${{ matrix.os }}