Fix string conversion for pr query string

Author: oliviacrain

homu/server.py

@@ -341,7 +341,7 @@ def rollup(user_gh, state, repo_label, repo_cfg, repo):
         base_url = g.cfg['web'].get('canonical_url')
 
     if base_url:
-        pr_list = ','.join(x.num for x in successes)
+        pr_list = ','.join(str(x.num) for x in successes)
         body += '\n\n[Create a similar rollup]({}/queue/{}?prs={})'.format(base_url, repo_label, pr_list)
 
     try: