Set --proxy argument to node-gyp based on .apmrc

Pass through the proxy or https-proxy npm config value
to node-gyp so that it can download the headers correctly.
Remove unused method
Set proxy to node-gyp when deduping
Respect strict SSL setting in dedupe command
Merge pull request #192 from atom/ks-set-proxy-to-node-gyp

Pass proxy setting through to node-gyp