Added Java 15 & Windows

.github/workflows/gradle.yml

@@ -1,15 +1,22 @@
 # This workflow will build a Java project with Gradle
 # For more information see: https://help.github.com/actions/language-and-framework-guides/building-and-testing-java-with-gradle
 
-name: Java CI with Gradle
+name: build
 
 on: [pull_request, push]
 
 jobs:
   build:
-
-    runs-on: ubuntu-latest
-
+    strategy:
+      matrix:
+        # Use these Java versions
+        java: [
+          1.8,  # Minimum supported by Minecraft
+          15    # Latest version
+        ]
+        # and run on both Linux and Windows
+        os: [ubuntu-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2
     - name: Set up JDK 1.8