Upgraded to http-proxy 1.0.
https://github.com/nodejitsu/node-http-proxy/blob/master/UPGRADING.md
Merge pull request #4 from garryyao/fix/http-proxy

This patch upgraded the proxy middleware to use the new http-proxy API.
Respond with a 500 for proxy error.
Updated all dependencies to use current latest major version.
v0.2.4