Update travis environment to trusty for newer cmake
Update travis environment to trusty for newer cmake

ClausSteuer/ParallelBottomUpBalancedOctreeBuilder,ClausSteuer/ParallelBottomUpBalancedOctreeBuilder,ClausSteuer/ParallelBottomUpBalancedOctreeBuilder,ClausSteuer/ParallelBottomUpBalancedOctreeBuilder