Strip refs/tags/ from release tarball name

Github does not expose the raw tag id, only the full ref. This is
actually how Github recommends doing this:
https://github.community/t/how-to-get-just-the-tag-name/16241/7

.github/workflows/release.yml

@@ -38,12 +38,15 @@ jobs:
           release_name: Release ${{ github.ref }}
           draft: true
           prerelease: false
+      - name: Get the tag name
+        id: tag_name
+        run: echo ::set-output name=tag::${GITHUB_REF#refs/tags/}
       - name: Upload Release Asset
         uses: actions/upload-release-asset@v1
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
           upload_url: ${{ steps.create_release.outputs.upload_url }}
           asset_path: ./.output/liquidprompt.tar.gz
-          asset_name: liquidprompt-${{ github.ref }}.tar.gz
+          asset_name: liquidprompt-${{ steps.tag_name.outputs.tag }}.tar.gz
           asset_content_type: application/gzip