Fix release script (#74)

Author: GuLinux

scripts/release-travis.py

@@ -25,7 +25,7 @@
     all_pulls = [pr for pr in repo.get_pulls(state='closed', sort='updated')]
     all_pulls.reverse()
     for merged_pr in all_pulls:
-        if pr.merge_commit_sha == commit_id:
+        if merged_pr.merge_commit_sha == commit_id:
             pr = merged_pr