title: Node.js ERROR Error: Cannot find module 'bluebird'
body: <p>When I try this,it throw an error,how can I solve it?</p>
  
  <pre><code>$ hexo generate
  ERROR Error: Cannot find module 'bluebird'
      at Function.Module._resolveFilename (module.js:338:15)
      at Function.Module._load (module.js:280:25)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at Object.&lt;anonymous&gt; (/Users/lihz/blog/node_modules/hexo/lib/hexo/index.js:3:15)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at /usr/local/lib/node_modules/hexo-cli/lib/index.js:73:18
      at tryCatcher (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/util.js:26:23)
      at Promise._settlePromiseFromHandler (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/promise.js:489:31)
      at Promise._settlePromiseAt (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/promise.js:565:18)
      at Promise._settlePromises (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/promise.js:681:14)
  Unhandled rejection TypeError: Cannot call method 'then' of undefined
      at /usr/local/lib/node_modules/hexo-cli/lib/index.js:82:22
      at tryCatcher (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/util.js:26:23)
      at Promise._settlePromiseFromHandler (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/promise.js:489:31)
      at Promise._settlePromiseAt (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/promise.js:565:18)
      at Async._drainQueue (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/async.js:128:12)
      at Async._drainQueues (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/async.js:133:10)
      at Async.drainQueues (/usr/local/lib/node_modules/hexo-cli/node_modules/bluebird/js/main/async.js:15:14)
      at process._tickCallback (node.js:442:13)
  </code></pre>