Fixed travis

Author: mannprerak2

.github/workflows/test-package.yml

@@ -19,7 +19,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        sdk: [2.12.0]
+        sdk: [2.13.0-211.6.beta] # TODO: revert to 2.13.
     steps:
       - uses: actions/checkout@v2
       - uses: dart-lang/[email protected]
@@ -43,7 +43,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: dart-lang/[email protected]
         with:
-          sdk: 2.12.0
+          sdk: 2.13.0-211.6.beta # TODO: revert to 2.13.
       - name: Install dependencies
         run: dart pub get
       - name: Install libclang-10-dev