Just like in node-sass, would be nice to read both IOJS_ORG_MIRROR and NODEJS_ORG_MIRROR (and their deprecated version) also from npm config settings. With this would be also possible to set its value in .npmrc file.

The change is really easy to do: just insert these variables in their respectives if/else chains:

• process.env.npm_config_iojs_org_mirror
• process.env.npm_config_nvm_iojs_org_mirror
• process.env.npm_config_nodejs_org_mirror
• process.env.npm_config_nvm_nodejs_org_mirror

I can do a pull request if you will.

Thanks in advance!