Build Failure in both Ubuntu 14.4 and Windows 7

[caunion]

Actually I solved the this problem, but still don't know if this comes from update of Jekyll or something else.
I tried to build this template under Ubuntu 14.4 (Ruby 2.1 + Jekyll 2.5.3) and Windows (Ruby 1.9/2.0 + Jekyll 2.5.3), both of which gives plugin-load error:

xiaoke@caunion:~/Travelogue$ jekyll serve
Configuration file: /home/xiaoke/Travelogue/_config.yml
/usr/local/lib/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:121:in `require': cannot load such file -- jekyll-sitemap (LoadError)
        from /usr/local/lib/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:121:in `require'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:29:in `block in require_gems'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:26:in `each'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:26:in `require_gems'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:19:in `conscientious_require'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/site.rb:79:in `setup'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/site.rb:41:in `initialize'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/commands/build.rb:29:in `new'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/commands/build.rb:29:in `process'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/commands/serve.rb:26:in `block (2 levels) in init_with_program'
        from /var/lib/gems/2.1.0/gems/mercenary-0.3.5/lib/mercenary/command.rb:220:in `call'
        from /var/lib/gems/2.1.0/gems/mercenary-0.3.5/lib/mercenary/command.rb:220:in `block in execute'
        from /var/lib/gems/2.1.0/gems/mercenary-0.3.5/lib/mercenary/command.rb:220:in `each'
        from /var/lib/gems/2.1.0/gems/mercenary-0.3.5/lib/mercenary/command.rb:220:in `execute'
        from /var/lib/gems/2.1.0/gems/mercenary-0.3.5/lib/mercenary/program.rb:42:in `go'
        from /var/lib/gems/2.1.0/gems/mercenary-0.3.5/lib/mercenary.rb:19:in `program'
        from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/bin/jekyll:20:in `<top (required)>'
        from /usr/local/bin/jekyll:23:in `load'
        from /usr/local/bin/jekyll:23:in `<main>'

Solution:
After inspection, I found the loading process crashed when loading "jekyll-sitemap". So users who meet similar problem can solve this by

gem install jekyll-sitemap

I'm not sure why this plugin has not been included, given that I followed standard jekyll install process. Is this plugin just removed from required dependencies or it was not since the beginning? If it is the latter, I think it might be a good idea to note this in README or somewhere.

This little problem is quite annoying for jekyll new users like me, since "--verbose" parameter will not output the "Jekyll.logger.debug" info and there is nowhere for me to find the log file to know what specific plugin has failed to load (If there is, pls tell me). My solution is to dump all loaded plugin to a file.