Update flutter.yml (#18)

* Update flutter.yml

* Update flutter.yml

Author: hoc081098

.github/workflows/flutter.yml

@@ -9,16 +9,22 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    
+    strategy:
+      matrix:
+        flutter-channel: [ 'stable', 'beta' ]
+    
     steps:
       - uses: actions/checkout@v2
 
-      - uses: actions/setup-java@v1
+      - uses: actions/setup-java@v2
         with:
-          java-version: '12.x'
+          distribution: 'zulu'
+          java-version: '11'
 
       - uses: subosito/flutter-action@v1
         with:
-          channel: 'beta'
+          channel: ${{ flutter-channel }}
 
       - name: Print Dart SDK version
         run: dart --version