Latest setup, test on oldest supported SDK (#110)

diff --git a/.github/workflows/test-package.yml b/.github/workflows/test-package.yml
index e5e47ea..36c2478 100644
--- a/.github/workflows/test-package.yml
+++ b/.github/workflows/test-package.yml
@@ -23,9 +23,9 @@
         sdk: [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 }}
       - id: install
         name: Install dependencies
         run: dart pub get
@@ -46,12 +46,12 @@
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        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 }}
       - id: install
         name: Install dependencies
         run: dart pub get