title: node-sass throw error when upgrade node to 4.0.0
body: <p>i'm developing an ionic app, and i use sass.
  when i upgrade my node version to 4.0.0, there is an error throw out about node-sass.
  the error is blow:</p>
  
  <pre><code>ionic $ /Applications/My-Project/nearbook/nearbooks_ionic/node_modules/gulp-sass/node_modules/node-sass/lib/index.js:22
      throw new Error('`libsass` bindings not found. Try reinstalling `node-sass
            ^
  Error: `libsass` bindings not found. Try reinstalling `node-sass`?
      at getBinding (/Applications/My-Project/nearbook/nearbooks_ionic/node_modules/gulp-sass/node_modules/node-sass/lib/index.js:22:11)
      at Object.&lt;anonymous&gt; (/Applications/My-Project/nearbook/nearbooks_ionic/node_modules/gulp-sass/node_modules/node-sass/lib/index.js:188:23)
      at Module._compile (module.js:460:26)
      at Object.Module._extensions..js (module.js:478:10)
      at Module.load (module.js:355:32)
      at Function.Module._load (module.js:310:12)
      at Module.require (module.js:365:17)
      at require (module.js:384:17)
      at Object.&lt;anonymous&gt; (/Applications/My-Project/nearbook/nearbooks_ionic/node_modules/gulp-sass/index.js:3:17)
      at Module._compile (module.js:460:26)
  </code></pre>
  
  <p>i have tried to reinstall all my node_modules (i delete node_modules folder and rerun node install) or run <code>node rebuild node-sass</code> but it still doesn't work.</p>
  
  <p>when i downgrade my node version to 0.12.7 and reinstall all node_modules, my problem solved.</p>
  
  <p>so i guess there is something wrong when node 4.0 compiling node-sass.</p>
  
  <p>Anyone know how to fix this?</p>