title: I have a issue with npm proxy
body: <p>I have a problem with proxy services when i need to install any package i get this error:
  ```
  C:\Users\ihab\Desktop\myApp\myApp>npm install -g npm@latest
  npm ERR! code ENOTFOUND
  npm ERR! errno ENOTFOUND
  npm ERR! network request to <a href="http://registry.npmjs.org/npm" rel="nofollow noreferrer">http://registry.npmjs.org/npm</a> failed, reason: getadd
  rinfo ENOTFOUND proxy_host proxy_host:80
  npm ERR! network This is a problem related to network connectivity.
  npm ERR! network In most cases you are behind a proxy or have bad network settin
  gs.
  npm ERR! network
  npm ERR! network If you are behind a proxy, please make sure that the
  npm ERR! network 'proxy' config is set properly.  See: 'npm help config'</p>
  
  <p>npm ERR! A complete log of this run can be found in:
  npm ERR!     C:\Users\ihab\AppData\Roaming\npm-cache_logs\2017-11-15T13_49_08_4
  73Z-debug.log</p>
  
  <p>C:\Users\ihab\Desktop\myApp\myApp>npm --registry <a href="http://registry.cnpmjs.org" rel="nofollow noreferrer">http://registry.cnpmjs.org</a> info
   underscore
  npm ERR! code ENOTFOUND
  npm ERR! errno ENOTFOUND
  npm ERR! syscall getaddrinfo
  npm ERR! network getaddrinfo ENOTFOUND proxy_host proxy_host:80
  npm ERR! network This is a problem related to network connectivity.
  npm ERR! network In most cases you are behind a proxy or have bad network settin
  gs.
  npm ERR! network
  npm ERR! network If you are behind a proxy, please make sure that the
  npm ERR! network 'proxy' config is set properly.  See: 'npm help config'</p>
  
  <p>npm ERR! A complete log of this run can be found in:
  npm ERR!     C:\Users\ihab\AppData\Roaming\npm-cache_logs\2017-11-15T13_51_14_6
  81Z-debug.log
  ```
  any solution for this problem please</p>