👷‍♂️ Use JDK 11 for build tests

Author: AlexV525

.github/workflows/build_test.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: actions/checkout@v1
       - uses: actions/setup-java@v1
         with:
-          java-version: '8.x'
+          java-version: '11.x'
       - uses: subosito/flutter-action@v1
         with:
           channel: 'stable'
@@ -38,7 +38,7 @@ jobs:
       - uses: actions/checkout@v1
       - uses: actions/setup-java@v1
         with:
-          java-version: '8.x'
+          java-version: '11.x'
       - uses: subosito/flutter-action@v1
         with:
           channel: 'stable'