title: jekyll plugin not working on local machine
body: <p>I have developed a simple filter for jekyll liquid module, and put the code in _plugins directory. but when I run jekyll the plugin doesn't work.</p>
  
  <p>here is the directory that I run jekyll:
  <a href="https://github.com/alishir/alishir.github.io/tree/dev" rel="nofollow">https://github.com/alishir/alishir.github.io/tree/dev</a> </p>
  
  <p>here is the plugin code, it return simple string just for test:
  <a href="https://github.com/alishir/alishir.github.io/blob/dev/_plugins/PersianDate.rb" rel="nofollow">https://github.com/alishir/alishir.github.io/blob/dev/_plugins/PersianDate.rb</a></p>