Another flake8 fix

Author: oliviacrain

homu/server.py

@@ -342,8 +342,8 @@ def rollup(user_gh, state, repo_label, repo_cfg, repo):
 
     if base_url:
         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))
+        link = '{}/queue/{}?prs={}'.format(base_url, repo_label, pr_list)
+        body += '\n\n[Create a similar rollup]({})'.format(link)
 
     try:
         pull = base_repo.create_pull(