Fix test failure re: "Module._cache.hasOwnProperty is not a function"
Fix test failure re: "Module._cache.hasOwnProperty is not a function"

Example build failure:
https://ci.appveyor.com/project/Atom/atom/build/job/fvtxos5ys6a5lek1#L634

As of Node 8.0.0, Module._cache.hasOwnProperty is no longer a function:
https://github.com/nodejs/node/commit/https://github.com/nodejs/node/commit/403b89e72b6367934ca3c36d389ce0f3214ffbf5

andrewleverette/atom,PKRoma/atom,t9md/atom,andrewleverette/atom,t9md/atom,PKRoma/atom,atom/atom,liuderchi/atom,Mokolea/atom,stinsonga/atom,t9md/atom,liuderchi/atom,stinsonga/atom,liuderchi/atom,liuderchi/atom,atom/atom,stinsonga/atom,Mokolea/atom,PKRoma/atom,atom/atom,andrewleverette/atom,Mokolea/atom,stinsonga/atom,brettle/atom,brettle/atom,brettle/atom