Update `.travis.yml`
Update `.travis.yml`

* Make minor improvements.
* Redirect all output from `export $(cat .to_export_back)` to
  `/dev/null` in order to prevent `export` from leaking the access
  token in the case when, for some odd reason, the `.to_export_back`
  file is not created.

atyenoria/server-configs-apache,johnnyicarus/server-configs-apache,walterebert/server-configs-apache,voku/server-configs-apache,johnnyicarus/server-configs-apache,blackmoral/server-configs-apache,blackmoral/server-configs-apache,atyenoria/server-configs-apache,Gillespie59/server-configs-apache,walterebert/server-configs-apache,h5bp/server-configs-apache,StephanieMak/server-configs-apache,sengkoil/server-configs-apache,voku/server-configs-apache,Gillespie59/server-configs-apache,sengkoil/server-configs-apache,StephanieMak/server-configs-apache