Travis: use GCC 4.8
Travis: use GCC 4.8

hassy/artillery,shoreditch-ops/artillery,shoreditch-ops/artillery-core,hassy/artillery-core,shoreditch-ops/artillery,erikerikson/artillery-core,hassy/artillery,erikerikson/artillery-core,hassy/artillery-core,shoreditch-ops/artillery-core,hassy/artillery,shoreditch-ops/artillery