Print dart version in CI job (#54)

diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index 0ed5c5a..36eb913 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -19,6 +19,9 @@
     steps:
       - uses: actions/checkout@v2
 
+      - name: Print Dart version
+        run: dart --version
+
       - name: pub get
         run: pub get