Add node v4.0 to the test matrix
Add node v4.0 to the test matrix

vincent1988/underscore,jdelbello/underscore,jashkenas/underscore,documentcloud/underscore,keepgoingwm/underscore,huangnan1/2016gitStudy,akre54/underscore,jridgewell/underscore,akre54/underscore,rlugojr/underscore,documentcloud/underscore,jpalomar/underscore,tnga/underscore-es,keepgoingwm/underscore,vincent1988/underscore,jridgewell/underscore,platinumazure/underscore,jpalomar/underscore,tnga/underscore-es,platinumazure/underscore,rlugojr/underscore,jashkenas/underscore,huangnan1/2016gitStudy,jdelbello/underscore