title: Can't install firebase-tools on ubuntu 16.04
body: <p>i'm trying to install firebase-tools in ubuntu (16.04) but i get an error </p>
  
  <p>after i execute the command line:</p>
  
  <pre><code>npm install -g firebase-tools
  </code></pre>
  
  <p>The error:</p>
  
  <pre><code>npm ERR! tar.unpack untar error /home/rezk/.npm/firebase-tools/3.2.1/package.tgz
  </code></pre>
  
  <p>npm ERR! Linux 4.4.0-59-generic
  npm ERR! argv "/usr/bin/nodejs" "/usr/bin/npm" "install" "-g" "firebase-tools"
  npm ERR! node v4.4.7
  npm ERR! npm  v2.15.8
  npm ERR! path /usr/lib/node_modules/firebase-tools
  npm ERR! code EACCES
  npm ERR! errno -13
  npm ERR! syscall mkdir</p>
  
  <p>npm ERR! Error: EACCES: permission denied, mkdir '/usr/lib/node_modules/firebase-tools'
  npm ERR!     at Error (native)
  npm ERR!  { [Error: EACCES: permission denied, mkdir '/usr/lib/node_modules/firebase-tools']
  npm ERR!   errno: -13,
  npm ERR!   code: 'EACCES',
  npm ERR!   syscall: 'mkdir',
  npm ERR!   path: '/usr/lib/node_modules/firebase-tools',
  npm ERR!   fstream_type: 'Directory',
  npm ERR!   fstream_path: '/usr/lib/node_modules/firebase-tools',
  npm ERR!   fstream_class: 'DirWriter',
  npm ERR!   fstream_stack: 
  npm ERR!    [ '/usr/lib/node_modules/npm/node_modules/fstream/lib/dir-writer.js:35:25',
  npm ERR!      '/usr/lib/node_modules/npm/node_modules/mkdirp/index.js:47:53',
  npm ERR!      'FSReqWrap.oncomplete (fs.js:82:15)' ] }
  npm ERR! 
  npm ERR! Please try running this command again as root/Administrator.</p>
  
  <p>npm ERR! Please include the following file with any support request:
  npm ERR!     /home/rezk/npm-debug.log</p>
  
  <p>how could i solve that?
  Note: i have installed Node.js </p>