Syntax error, undefined sequence

I've installed all the requirements for the jekyll image tag plugin but when I build my site I receive an error message and no files are created.

I don't think it's an issue with the plugin. I'm a Ruby-Newbie, and I don't know how to interpret the error. Hopefully you can point me in the right direction.

Error message is posted below:

MacBook-Pro:wesleymiller.com wesleymiller$ jekyll build
Configuration file: /Users/wesleymiller/Dropbox/Sites/wesleymiller.com/_config.yml
/Library/Ruby/Site/1.8/rubygems/core_ext/kernel_require.rb:55:in `gem_original_require': /Users/wesleymiller/Dropbox/Sites/wesleymiller.com/_plugins/image_tag.rb:39: undefined (?...) sequence: /^(?:(?<preset>[^\s.:\/]+)\s+)?(?<image_src>[^\s]+\.[a-zA-Z0-9]{3,4})\s*(?<html_attr>[\s\S]+)?$/ (SyntaxError)
/Users/wesleymiller/Dropbox/Sites/wesleymiller.com/_plugins/image_tag.rb:58: undefined (?...) sequence: /^(?:(?<width>\d+)|auto)(?:x)(?:(?<height>\d+)|auto)$/
/Users/wesleymiller/Dropbox/Sites/wesleymiller.com/_plugins/image_tag.rb:70: undefined (?...) sequence: /(?<attr>[^\s="]+)(?:="(?<value>[^"]+)")?\s?/
    from /Library/Ruby/Site/1.8/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /Library/Ruby/Gems/1.8/gems/jekyll-1.2.1/bin/../lib/jekyll/site.rb:77:in `setup'
    from /Library/Ruby/Gems/1.8/gems/jekyll-1.2.1/bin/../lib/jekyll/site.rb:76:in `each'
    from /Library/Ruby/Gems/1.8/gems/jekyll-1.2.1/bin/../lib/jekyll/site.rb:76:in `setup'
    from /Library/Ruby/Gems/1.8/gems/jekyll-1.2.1/bin/../lib/jekyll/site.rb:75:in `each'
    from /Library/Ruby/Gems/1.8/gems/jekyll-1.2.1/bin/../lib/jekyll/site.rb:75:in `setup'
    from /Library/Ruby/Gems/1.8/gems/jekyll-1.2.1/bin/../lib/jekyll/site.rb:26:in `initialize'
    from /Library/Ruby/Gems/1.8/gems/jekyll-1.2.1/bin/../lib/jekyll/commands/build.rb:5:in `new'
    from /Library/Ruby/Gems/1.8/gems/jekyll-1.2.1/bin/../lib/jekyll/commands/build.rb:5:in `process'
    from /Library/Ruby/Gems/1.8/gems/jekyll-1.2.1/bin/jekyll:73
    from /Library/Ruby/Gems/1.8/gems/commander-4.1.5/lib/commander/command.rb:180:in `call'
    from /Library/Ruby/Gems/1.8/gems/commander-4.1.5/lib/commander/command.rb:180:in `call'
    from /Library/Ruby/Gems/1.8/gems/commander-4.1.5/lib/commander/command.rb:155:in `run'
    from /Library/Ruby/Gems/1.8/gems/commander-4.1.5/lib/commander/runner.rb:402:in `run_active_command'
    from /Library/Ruby/Gems/1.8/gems/commander-4.1.5/lib/commander/runner.rb:66:in `run!'
    from /Library/Ruby/Gems/1.8/gems/commander-4.1.5/lib/commander/delegates.rb:7:in `run!'
    from /Library/Ruby/Gems/1.8/gems/commander-4.1.5/lib/commander/import.rb:10
    from /usr/bin/jekyll:23
MacBook-Pro:wesleymiller.com wesleymiller$

Thanks.

robwierzbowski / jekyll-image-tag

Syntax error, undefined sequence #7