dev-util/heroku: Re-generate manifest

```
2013-11-04 20:49:04 (112 KB/s) - ‘/usr/portage/distfiles/heroku-client.tgz’ saved [665340/665340]

!!! Fetched file: heroku-client.tgz VERIFY FAILED!
!!! Reason: Filesize does not match recorded size
!!! Got:      665340
!!! Expected: 662288
Refetching... File renamed to '/usr/portage/distfiles/heroku-client.tgz._checksum_failure_.l_68s6'
```