Set missing GITHUB_REF_SLUG env variable in gorelease action

.github/workflows/goreleaser.yml

@@ -9,21 +9,23 @@ jobs:
   goreleaser:
     runs-on: ubuntu-latest
     steps:
-      -
-        name: Checkout
+      - name: Checkout
         uses: actions/checkout@v2
         with:
           fetch-depth: 0
-      -
-        name: Set up Go
+      - name: Set up Go
         uses: actions/setup-go@v2
         with:
           go-version: 1.14
-      -
-        name: Run GoReleaser
+
+      - name: Set GITHUB_REF_SLUG
+        id: set_github_ref_slug
+        run: echo ::set-env name=GITHUB_REF_SLUG::${GITHUB_REF#refs/tags/}
+
+      - name: Run GoReleaser
         uses: goreleaser/goreleaser-action@v2
         with:
           version: latest
           args: release --rm-dist
         env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}