title: Error: Cannot find module 'gulp-uglifyjs' with "gulp watch
body: <p>I´m in my project folder on my terminal, and: </p>
  
  <p>if I extecute:</p>
  
  <pre><code>     gulp -v
  </code></pre>
  
  <p>I get: </p>
  
  <pre><code>[15:47:15] CLI version 3.9.0
  [15:47:15] Local version 3.9.0
  </code></pre>
  
  <p>if I excute: </p>
  
  <pre><code> gulp watch
  </code></pre>
  
  <p>I get: </p>
  
  <pre><code>Error: Cannot find module 'gulp-uglifyjs'
     at Function.Module._resolveFilename (module.js:338:15)
     at Function.Module._load (module.js:289:25)
     at Module.require (module.js:366:17)
     at require (module.js:385:17)
     at Object.&lt;anonymous&gt;    (/Applications/XAMPP/xamppfiles/htdocs/last/gulpfile.js:3:14)
     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:313:12)
     at Module.require (module.js:366:17)
     at require (module.js:385:17)
  </code></pre>
  
  <p>Then, I search in the gulpfile.js 3:14 and I see this: </p>
  
  <pre><code>var uglify = require('gulp-uglifyjs');
  </code></pre>
  
  <p>I was read about this, a lot people say "oh, do npm install", I do, and after make npm -v I get this: </p>
  
  <pre><code> 3.3.12
  </code></pre>
  
  <p>I was trying with a lot commands, but I dont know what happen. Maybe gulpfile.js? </p>
  
  <p>Maybe I forgot a dependencie? </p>