dev-util/heroku: Fix does not match size

```
2013-10-11 11:28:23 (479 KB/s) - ‘/usr/portage/distfiles/heroku-client.tgz’ saved [662288/662288]

!!! Fetched file: heroku-client.tgz VERIFY FAILED!
!!! Reason: Filesize does not match recorded size
!!! Got:      662288
!!! Expected: 659086
Refetching... File renamed to '/usr/portage/distfiles/heroku-client.tgz._checksum_failure_.obcyof'
```