Travisimprovements1

Suggested minor improvements to the travis config; also just testing I understand the github workflow...
There were three things:
* no need to run cat /etc/hosts as root (best practice being not to run as root unless absolutely necessary)
* making the individual sed commands more readable, separating arguments from the command (2 i foo instead of 2ifoo)
* re-ordering the hostnames into a more consistent order

I'd quite like to keep the first change (removing "sudo" from cat), but am happy to revert the rest since they're just a style issue.