title: cross-env issue when running "npm run dev" for vue-cli
body: <p>I'm with Centos7, installed on VirtualBox (true OS: Windows 7).</p>
  
  <ul>
  <li>Node version: 6.10.3</li>
  <li>Npm version: 3.10.10</li>
  </ul>
  
  <p>I installed vue-cli, like this:</p>
  
  <pre><code>sudo npm install -g vue-cli
  </code></pre>
  
  <p>Then I created a new vue project, like this:</p>
  
  <pre><code>sudo vue init webpack-simple mynewproject
  </code></pre>
  
  <p>But I get an error when running "npm run dev":</p>
  
  <pre><code>&gt; mynewproject@1.0.0 dev /var/www/html/mynewproject
  &gt; cross-env NODE_ENV=development webpack-dev-server --open --hot
  
  sh: cross-env : commande introuvable
  
  npm ERR! Linux 3.10.0-514.el7.x86_64
  npm ERR! argv "/usr/bin/node" "/usr/bin/npm" "run" "dev"
  npm ERR! node v6.10.3
  npm ERR! npm  v3.10.10
  npm ERR! file sh
  npm ERR! code ELIFECYCLE
  npm ERR! errno ENOENT
  npm ERR! syscall spawn
  npm ERR! vuetest@1.0.0 dev: `cross-env NODE_ENV=development webpack-dev-server --open --hot`
  npm ERR! spawn ENOENT
  npm ERR!
  npm ERR! Failed at the mynewproject@1.0.0 dev script 'cross-env NODE_ENV=development webpack-dev-server --open --hot'.
  npm ERR! Make sure you have the latest version of node.js and npm installed.
  npm ERR! If you do, this is most likely a problem with the vuetest package,
  npm ERR! not with npm itself.
  npm ERR! Tell the author that this fails on your system:
  npm ERR!     cross-env NODE_ENV=development webpack-dev-server --open --hot
  npm ERR! You can get information on how to open an issue for this project with:
  npm ERR!     npm bugs vuetest
  npm ERR! Or if that isn't available, you can get their info via:
  npm ERR!     npm owner ls vuetest
  npm ERR! There is likely additional logging output above.
  
  npm ERR! Please include the following file with any support request:
  npm ERR!     /var/www/html/mynewproject/npm-debug.log
  </code></pre>
  
  <p>Does anyone know how to fix it?</p>