Fix tests on Node 0.12.
Fix tests on Node 0.12.

myndzi/node-source-map-support,kpdecker/node-source-map-support,peter-fu/node-source-map-support,peter-fu/node-source-map-support,mprobst/node-source-map-support,tanem/node-source-map-support,tugend/node-source-map-support,mprobst/node-source-map-support,merqlove/node-source-map-support,evanw/node-source-map-support,evanw/node-source-map-support,tugend/node-source-map-support,myndzi/node-source-map-support,kpdecker/node-source-map-support,merqlove/node-source-map-support,tanem/node-source-map-support