Remove Jekyll on-the-fly Gemfile parsing.

This was be the best way to get the latest version on GitHub Pages,
but it's annoying, as it will break all Builds after a new release.

We're going with [plan B](https://jekyllrb.com/docs/github-pages/)
now. 😄

Author: bascht

Gemfile

@@ -2,9 +2,8 @@ source 'https://rubygems.org'
 
 require 'json'
 require 'open-uri'
-versions = JSON.parse(open('https://pages.github.com/versions.json').read)
 
 gem 'jekyll', '~> 3.3'
-gem 'github-pages', versions['github-pages'], group: :jekyll_plugin
+gem 'github-pages', group: :jekyll_plugin
 gem 'jekyll-theme-cayman'
 gem 'nokogiri'

Gemfile.lock

@@ -164,7 +164,7 @@ GEM
     minitest (5.10.2)
     multipart-post (2.0.0)
     net-dns (0.8.0)
-    nokogiri (1.7.1)
+    nokogiri (1.7.2)
       mini_portile2 (~> 2.1.0)
     octokit (4.7.0)
       sawyer (~> 0.8.0, >= 0.5.3)
@@ -176,7 +176,7 @@ GEM
       ffi (>= 0.5.0)
     rouge (1.11.1)
     safe_yaml (1.0.4)
-    sass (3.4.23)
+    sass (3.4.24)
     sawyer (0.8.1)
       addressable (>= 2.3.5, < 2.6)
       faraday (~> 0.8, < 1.0)
@@ -193,7 +193,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  github-pages (= 138)
+  github-pages
   jekyll (~> 3.3)
   jekyll-theme-cayman
   nokogiri