expand travis node version coverage
expand travis node version coverage

lastguest/levelup,djchie/levelup,roppa/levelup,timkuijsten/levelup,toddself/levelup,JTKnox91/levelup,lastguest/levelup,Level/levelup,JTKnox91/levelup,roppa/levelup,toddself/levelup,djchie/levelup,timkuijsten/levelup