Update .tx/config to new servers

We need to update the host in `.tx/config` from http://www.transifex.net to https://www.transifex.com.

Otherwise it complains when using the cli client, and our docs use this host anyway:
http://docs.ckan.org/en/latest/release-process.html#doing-a-beta-release

```
Hostname http://www.transifex.net should be changed to https://www.transifex.com.
Change it now? [Y/n]
```