Update whitelist

I see this list:

http://pages.github.com/versions

However comparing it against

pages-gem/lib/github-pages/plugins.rb

Lines 22 to 41 in fb5c3f2

	jekyll-coffeescript
	jekyll-commonmark-ghpages
	jekyll-feed
	jekyll-gist
	jekyll-github-metadata
	jekyll-paginate
	jekyll-redirect-from
	jekyll-seo-tag
	jekyll-sitemap
	jekyll-avatar
	jemoji
	jekyll-mentions
	jekyll-relative-links
	jekyll-optional-front-matter
	jekyll-readme-index
	jekyll-default-layout
	jekyll-titles-from-headings
	jekyll-include-cache
	jekyll-octicons
	jekyll-remote-theme

reveals that these are missing:

• jekyll-include-cache
• jekyll-octicons

[parkr]

The gems that are reported via site.github.versions (which pages.github.com uses) is here:

pages-gem/lib/github-pages/dependencies.rb

Lines 8 to 49 in fb5c3f2

	VERSIONS = {
	# Jekyll
	"jekyll" => "3.7.4",
	"jekyll-sass-converter" => "1.5.2",
	# Converters
	"kramdown" => "1.17.0",
	"jekyll-commonmark-ghpages" => "0.1.5",
	# Misc
	"liquid" => "4.0.0",
	"rouge" => "2.2.1",
	"github-pages-health-check" => "1.8.1",
	# Plugins
	"jekyll-redirect-from" => "0.14.0",
	"jekyll-sitemap" => "1.2.0",
	"jekyll-feed" => "0.11.0",
	"jekyll-gist" => "1.5.0",
	"jekyll-paginate" => "1.1.0",
	"jekyll-coffeescript" => "1.1.1",
	"jekyll-seo-tag" => "2.5.0",
	"jekyll-github-metadata" => "2.9.4",
	"jekyll-avatar" => "0.6.0",
	"jekyll-remote-theme" => "0.3.1",
	# Plugins to match GitHub.com Markdown
	"jemoji" => "0.10.1",
	"jekyll-mentions" => "1.4.1",
	"jekyll-relative-links" => "0.5.3",
	"jekyll-optional-front-matter" => "0.3.0",
	"jekyll-readme-index" => "0.2.0",
	"jekyll-default-layout" => "0.1.4",
	"jekyll-titles-from-headings" => "0.5.1",
	# Pin listen because it's broken on 2.1 & that's what we recommend.
	# https://github.com/guard/listen/pull/371
	"listen" => "3.1.5",
	# Pin activesupport because 5.0 is broken on 2.1
	"activesupport" => "4.2.10",
	}.freeze

You'll notice that those two gems are omitted here.