docs(travis): simplify test script, update node version
docs(travis): simplify test script, update node version

maksimr/karma,kahwee/karma,SamuelMarks/karma,kahwee/karma,pedrotcaraujo/karma,pedrotcaraujo/karma,pedrotcaraujo/karma,shirish87/karma,mprobst/karma,johnjbarton/karma,kahwee/karma,shirish87/karma,panrafal/karma,wesleycho/karma,Dignifiedquire/karma,pedrotcaraujo/karma,SamuelMarks/karma,mprobst/karma,ernsheong/karma,Dignifiedquire/karma,panrafal/karma,kahwee/karma,johnjbarton/karma,wesleycho/karma,Dignifiedquire/karma,david-garcia-nete/karma,maksimr/karma,ernsheong/karma,SamuelMarks/karma,johnjbarton/karma,wesleycho/karma,johnjbarton/karma,wesleycho/karma,ernsheong/karma,shirish87/karma,maksimr/karma,panrafal/karma,karma-runner/karma,karma-runner/karma,Dignifiedquire/karma,karma-runner/karma,mprobst/karma,karma-runner/karma,david-garcia-nete/karma,david-garcia-nete/karma