FIX: Modernise travis build matrix
FIX: Modernise travis build matrix

 - SS 3.6 works with PHP 7.1
 - PHP 5.3 testing is no longer feasible
 - Deprecated use of precise no longer needed

dhensby/silverstripe-docsviewer,silverstripe/silverstripe-docsviewer,silverstripe/silverstripe-docsviewer,dhensby/silverstripe-docsviewer