add automatic prerelase flagging

Author: alexlanz

.github/workflows/release.yml

@@ -21,7 +21,8 @@ jobs:
               owner: context.repo.owner,
               repo: context.repo.repo,
               tag_name: '${{ github.ref }}',
-              name: 'Release ${{ github.ref_name }}'
+              name: 'Release ${{ github.ref_name }}',
+              prerelease: '${{ github.ref_name }}'.includes('-')
             })
       - uses: aboutbits/github-actions-node/setup-and-install@v2
         with: