Update CI setup (#56)

diff --git a/.github/workflows/test-package.yml b/.github/workflows/test-package.yml
index 04eaf61..f81b025 100644
--- a/.github/workflows/test-package.yml
+++ b/.github/workflows/test-package.yml
@@ -19,11 +19,11 @@
     strategy:
       fail-fast: false
       matrix:
-        sdk: [dev]
+        sdk: [2.12.0, dev]
     steps:
       - uses: actions/checkout@v2
-      - uses: dart-lang/setup-dart@v0.1
+      - uses: dart-lang/setup-dart@v1.0
         with:
-          channel: ${{ matrix.sdk }}
+          sdk: ${{ matrix.sdk }}
       - name: Test
         run: ./tool/travis.sh