title: Gulp throwing cannot find module '.lib/source-map-generator'
body: <p>I have installed Gulp with Laravel and then installed Bootstrap sass for the project. Gulp can run other task but throws cannot find module '.lib/source-map-generator' when it arrives at the sass task. </p>
  
  <p>The following is the gulp error:</p>
  
  <pre><code>vagrant@homestead:~/Code/specflux$ gulp
  [08:55:46] Using gulpfile ~/Code/specflux/gulpfile.js
  [08:55:46] Starting 'default'...
  [08:55:46] Starting 'sass'...
  [08:55:46] 'sass' errored after 128 ms
  [08:55:46] Error: Cannot find module './lib/source-map-generator'
      at Function.Module._resolveFilename (module.js:337:15)
      at Function.Module._load (module.js:287:25)
      at Module.require (module.js:366:17)
      at require (module.js:385:17)
      at Object.&lt;anonymous&gt; (/home/vagrant/Code/specflux/node_modules/laravel-elixir/node_modules/gulp-sass/node_modules/vinyl-sourcemaps-apply/node_modules/source-map/source-map.js:6:30)
      at Module._compile (module.js:425:26)
      at Object.Module._extensions..js (module.js:432:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:311:12)
      at Module.require (module.js:366:17)
      at require (module.js:385:17)
  [08:55:46] Error in plugin 'run-sequence'
  Message:
      An error occured in task 'sass'.
  [08:55:46] Finished 'default' after 162 ms
  </code></pre>
  
  <p>The following is my gulpfile.js code:</p>
  
  <pre><code>var elixir = require('laravel-elixir');
  
  elixir(function(mix) {
     mix.sass('app.scss');
  });
  </code></pre>
  
  <p>There app.scss only has the following code:</p>
  
  <pre><code>@import "../../../vendor/bower_components/bootstrap-sass/assets/stylesheets/bootstrap";
  </code></pre>
  
  <p>How to fix the gulp error?</p>