chore: [Snyk] Security upgrade github-pages from 207 to 214 (#267)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-RUBY-KRAMDOWN-1087436

Co-authored-by: Tom Kerkhove <[email protected]>

Author: snyk-bot

docs/Gemfile

@@ -1,4 +1,4 @@
 source 'https://rubygems.org'
-gem 'github-pages', '>= 207', group: :jekyll_plugins
+gem 'github-pages', '>= 214', group: :jekyll_plugins
 gem 'nokogiri', '>= 1.11.4'
-gem 'jekyll-redirect-from', '>= 0.15.0', group: :jekyll_plugins
+gem 'jekyll-redirect-from', group: :jekyll_plugins