Exclude the line containing the version from the release body

And fix an embarassing case of undefined variables

.github/workflows/auto-release.yml

@@ -39,7 +39,7 @@ jobs:
             const changelog = require('fs').readFileSync('CHANGELOG.md', { encoding: 'utf-8' }).split('\n');
             const start = changelog.findIndex(line => line.startsWith('## '));
             const end = changelog.findIndex((line, index) => line.startsWith('## ') && index > start);
-            return changelog.slice(startIndex, endIndex).join('\n');
+            return changelog.slice(start + 1, end).join('\n').trim();
 
       - name: Create a release 🔖
         uses: actions/create-release@v1