Update go.yml

.github/workflows/go.yml

@@ -19,6 +19,7 @@ jobs:
     - name: Get dependencies
       run: |
         go get -v -t -d ./...
+        go get github.com/magefile/mage
         if [ -f Gopkg.toml ]; then
             curl https://raw.githubusercontent.com/golang/dep/master/install.sh | sh
             dep ensure