electron_mirror is not honored on OS X due to process.env being case-sensitive

[jsbeckma]

It looks like process.env is case-insensitive on Windows but case-sensitive on OS X. When download-chromedriver.js runs on OS X, the process.env.npm_* variables are lower case and therefore process.env.NPM_CONFIG_ELECTRON_MIRROR equates to undefined and baseUrl defaults to https://github.com/electron/electron/release/download/v.

-- steps to reproduce --

npm config set electron_mirror http://nothingtoseehere.com
node ./download-chromedriver.js

The above should fail on OS X but does not.

I'm using:

• OS X 10.11.6
• node 4.4.7 (I've also tested it on 6.4.0 and the issue still exists)
• npm 2.15.8

[jsbeckma]

Created #6
This is the first public project I've contributed to so I hope my etiquette is correct. Cheers.

[kevinsawicki]

Fixed by #6