Fix the Travis build
Fix the Travis build

The error was:

```
Setting up postgresql-9.4 (9.4.5-2.pgdg12.4+1) ...
Refused to start PostgreSQL 9.4, because PostgreSQL 9.1 is currently running! You should first stop 9.1 instance...
invoke-rc.d: initscript postgresql, action "start" failed.
dpkg: error processing postgresql-9.4 (--configure):
subprocess installed post-installation script returned error exit status 13
 ```

I tried `sudo apt-get remove postgresql` then, but:

```
Package postgresql is not installed, so not removed
0 upgraded, 0 newly installed, 0 to remove and 65 not upgraded.
```

So let's kill it less softly.

hammerlab/ketrew