fix workflow

Author: michimani

.github/workflows/release.yml

@@ -66,7 +66,7 @@ jobs:
       run: |
         pwd
         ls -al
-        url=$(cat artifact/url.txt)
+        url=$(cat url.txt)
         echo "##[set-output name=upload_url;]$url"
     - name: Check out code into the Go module directory
       uses: actions/checkout@v2