Fix postinstall on windows

[ianobermiller]

Creating a PR to test the appveyor build

[ryan-roemer]

@ianobermiller -- If appveyor doesn't like this another option is to just use npm programmatically in a Node script. Here's some totally unrelated code that looks for extra devDependencies that for Heroku only should be installed and then uses NPM programmatically to install them... https://github.com/FormidableLabs/full-stack-testing/blob/master/app/heroku/install.js

(Just in case it helps ;) )

[ianobermiller]

Probably running into this: nodejs/node-v0.x-archive#2318

[ianobermiller]

Yes!

[coveralls]

Coverage remained the same at 100.0% when pulling 5995703 on windows-build into 8a7a821 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling f0dc4a0 on windows-build into 8a7a821 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 23ab310 on windows-build into 8a7a821 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 06fc986 on windows-build into 5634b9f on master.