我正在尝试从命令行在Windows 7中安装npm。它返回此错误：
npm ERR! code ENOTFOUND
npm ERR! errno ENOTFOUND
npm ERR! network request to https://registry.npmjs.org/angular failed, reason: getaddrinfo ENOTFOUND registry.npmjs.org registry.npmjs.org:443
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 settings.
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'
如果这是代理问题，如何解决？