Debugging with mocha fail on Appveyor

I am using `devtool` to debug [`atom-keymap`](https://github.com/atom/atom-keymap). Although it success on Travis but it is failing on [**Appveyor**](https://ci.appveyor.com/project/torn4dom4n/atom-keymap/build/1.0.35):

```
Error:
C:\projects\atom-keymap\node_modules\mocha\bin\_mocha
Cannot find module 'C:\projects\atom-keymap\spec\fixtures'
at Module._resolveFilename (module.js:455:15)
at Function.Module._resolveFilename (C:\projects\atom-keymap\node_modules\electron\dist\resources\electron.asar\common\reset-search-paths.js:35:12)
at Function.Module._load (module.js:403:25)
at Module.require (module.js:483:17)
at require (internal/module.js:20:19)
at C:\projects\atom-keymap\node_modules\mocha\lib\mocha.js:222:27
at Array.forEach (native)
at Mocha.loadFiles (C:\projects\atom-keymap\node_modules\mocha\lib\mocha.js:219:14)
at Mocha.run (C:\projects\atom-keymap\node_modules\mocha\lib\mocha.js:487:10)
at Object. (C:\projects\atom-keymap\node_modules\mocha\bin\_mocha:458:18)
at Module._compile (module.js:556:32)
at Object.devtoolCompileModule (C:\projects\atom-keymap\node_modules\devtool\lib\require-hook.js:32:14)
at Module.load (module.js:473:32)
at tryModuleLoad (module.js:432:12)
at Function.Module._load (module.js:424:3)
at Module.require (module.js:483:17)
at require (internal/module.js:20:19)
at EventEmitter. (C:\projects\atom-keymap\node_modules\devtool\lib\preload.js:88:16)
at emitOne (events.js:96:13)
at EventEmitter.emit (events.js:188:7)
```