git initしなおしても速くならないんだなあ…
$ git push heroku master
Enumerating objects: 10021, done.
Counting objects: 100% (10021/10021), done.
Delta compression using up to 12 threads
Compressing objects: 100% (7590/7590), done.
Writing objects: 14% (1449/10021), 252.37 MiB | 704.00 KiB/s