Error in using Octopress pullquote, hope someone can help me

[Yuhang He]

Hi friends,

    I am blogging with Octopress framework. I am trying to use pullquote function in my blog. How ever I encounter the following error when I just follow the official site to input the quotes:

{% pullquote %}

When writing long-form posts, I find it helpful to include pull-quotes, which help

those scanning a post discern whether or not a post is helpful. It is important to 

note, {" pull-quotes are merely visual in presentation and should not appear twice in the text. "} That 

is why it is preferred to use a CSS only technique for styling pull-quotes.

{% endpullquote %}

  Then, when I ran rake generate command, it shows the following the error:

Liquid Exception: uninitialized constant Jekyll::PullquoteTag::RubyPants in _posts/test.markdown/#excerpt

jekyll 2.5.3 | Error:  uninitialized constant Jekyll::PullquoteTag::RubyPants

   I guess it might be jekyll version problem. Does anyone encounter the same problem with me? Any suggestion to debug this problem is super welcome.

Thanks.