Fix CHANGELOG parsing in release workflow

.github/workflows/release.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Get changes
         id: changelog
         run: |
-          pattern='0,/${{ github.ref }}/d;/[0-9]\+\.[0-9]\+\.[0-9]\+/Q'
+          pattern='0,/${GITHUB_REF#refs/tags/v}/d;/[0-9]\+\.[0-9]\+\.[0-9]\+/Q'
           echo ::set-output name=changelog::$(sed $pattern CHANGELOG.md | head -n -1 | tail -n +2)
       - name: Create release
         uses: actions/create-release@master