Gemfile{,.lock}: update dependencies, add webrick

webrick added due to github/pages-gem#752

closes #179

Author: classabbyamp

Gemfile

@@ -4,3 +4,5 @@ source "https://rubygems.org"
 
 git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
 gem 'github-pages', group: :jekyll_plugins
+
+gem "webrick", "~> 1.7"