Error in hexo deploy to heroku
<p>I am trying to do a hexo deploy to heroku, but this error shows up:</p>

<pre><code>    remote: Building source:        
remote: 
remote: -----&gt; Failed to detect set buildpack https://codon-buildpacks.s3.amazonaws.com/buildpacks/heroku/nodejs.tgz        
remote: More info: https://devcenter.heroku.com/articles/buildpacks#detection-failure        
remote: 
remote:  !     Push failed        
remote: Verifying deploy...        
remote: 
remote: !   Push rejected to pure-caverns-85771.        
remote: 
To git@heroku.com:pure-caverns-85771.git
 ! [remote rejected] master -&gt; master (pre-receive hook declined)
error: failed to push some refs to 'git@heroku.com:pure-caverns-85771.git'
</code></pre>

<p>I do have the <code>package.json</code> and I have install hexo-deployer-heroku pluggin.. any ideas? </p>