Add a Gemfile to pin Ruby dependencies (#1544)

Otherwise breaking changes in e.g. jekyll interface will render the
development environment broken.

Gemfile

@@ -0,0 +1,4 @@
+source 'https://rubygems.org'
+
+gem 'github-pages', '140'
+gem 'foreman'

Gemfile.lock

@@ -0,0 +1,203 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    activesupport (4.2.8)
+      i18n (~> 0.7)
+      minitest (~> 5.1)
+      thread_safe (~> 0.3, >= 0.3.4)
+      tzinfo (~> 1.1)
+    addressable (2.5.1)
+      public_suffix (~> 2.0, >= 2.0.2)
+    coffee-script (2.4.1)
+      coffee-script-source
+      execjs
+    coffee-script-source (1.12.2)
+    colorator (1.1.0)
+    ethon (0.10.1)
+      ffi (>= 1.3.0)
+    execjs (2.7.0)
+    faraday (0.12.1)
+      multipart-post (>= 1.2, < 3)
+    ffi (1.9.18)
+    foreman (0.84.0)
+      thor (~> 0.19.1)
+    forwardable-extended (2.6.0)
+    gemoji (3.0.0)
+    github-pages (140)
+      activesupport (= 4.2.8)
+      github-pages-health-check (= 1.3.4)
+      jekyll (= 3.4.3)
+      jekyll-avatar (= 0.4.2)
+      jekyll-coffeescript (= 1.0.1)
+      jekyll-default-layout (= 0.1.4)
+      jekyll-feed (= 0.9.2)
+      jekyll-gist (= 1.4.0)
+      jekyll-github-metadata (= 2.3.1)
+      jekyll-mentions (= 1.2.0)
+      jekyll-optional-front-matter (= 0.1.2)
+      jekyll-paginate (= 1.1.0)
+      jekyll-readme-index (= 0.1.0)
+      jekyll-redirect-from (= 0.12.1)
+      jekyll-relative-links (= 0.4.0)
+      jekyll-sass-converter (= 1.5.0)
+      jekyll-seo-tag (= 2.2.3)
+      jekyll-sitemap (= 1.0.0)
+      jekyll-swiss (= 0.4.0)
+      jekyll-theme-architect (= 0.0.4)
+      jekyll-theme-cayman (= 0.0.4)
+      jekyll-theme-dinky (= 0.0.4)
+      jekyll-theme-hacker (= 0.0.4)
+      jekyll-theme-leap-day (= 0.0.4)
+      jekyll-theme-merlot (= 0.0.4)
+      jekyll-theme-midnight (= 0.0.4)
+      jekyll-theme-minimal (= 0.0.4)
+      jekyll-theme-modernist (= 0.0.4)
+      jekyll-theme-primer (= 0.2.1)
+      jekyll-theme-slate (= 0.0.4)
+      jekyll-theme-tactile (= 0.0.4)
+      jekyll-theme-time-machine (= 0.0.4)
+      jekyll-titles-from-headings (= 0.1.5)
+      jemoji (= 0.8.0)
+      kramdown (= 1.13.2)
+      liquid (= 3.0.6)
+      listen (= 3.0.6)
+      mercenary (~> 0.3)
+      minima (= 2.1.1)
+      rouge (= 1.11.1)
+      terminal-table (~> 1.4)
+    github-pages-health-check (1.3.4)
+      addressable (~> 2.3)
+      net-dns (~> 0.8)
+      octokit (~> 4.0)
+      public_suffix (~> 2.0)
+      typhoeus (~> 0.7)
+    html-pipeline (2.6.0)
+      activesupport (>= 2)
+      nokogiri (>= 1.4)
+    i18n (0.8.4)
+    jekyll (3.4.3)
+      addressable (~> 2.4)
+      colorator (~> 1.0)
+      jekyll-sass-converter (~> 1.0)
+      jekyll-watch (~> 1.1)
+      kramdown (~> 1.3)
+      liquid (~> 3.0)
+      mercenary (~> 0.3.3)
+      pathutil (~> 0.9)
+      rouge (~> 1.7)
+      safe_yaml (~> 1.0)
+    jekyll-avatar (0.4.2)
+      jekyll (~> 3.0)
+    jekyll-coffeescript (1.0.1)
+      coffee-script (~> 2.2)
+    jekyll-default-layout (0.1.4)
+      jekyll (~> 3.0)
+    jekyll-feed (0.9.2)
+      jekyll (~> 3.3)
+    jekyll-gist (1.4.0)
+      octokit (~> 4.2)
+    jekyll-github-metadata (2.3.1)
+      jekyll (~> 3.1)
+      octokit (~> 4.0, != 4.4.0)
+    jekyll-mentions (1.2.0)
+      activesupport (~> 4.0)
+      html-pipeline (~> 2.3)
+      jekyll (~> 3.0)
+    jekyll-optional-front-matter (0.1.2)
+      jekyll (~> 3.0)
+    jekyll-paginate (1.1.0)
+    jekyll-readme-index (0.1.0)
+      jekyll (~> 3.0)
+    jekyll-redirect-from (0.12.1)
+      jekyll (~> 3.3)
+    jekyll-relative-links (0.4.0)
+      jekyll (~> 3.3)
+    jekyll-sass-converter (1.5.0)
+      sass (~> 3.4)
+    jekyll-seo-tag (2.2.3)
+      jekyll (~> 3.3)
+    jekyll-sitemap (1.0.0)
+      jekyll (~> 3.3)
+    jekyll-swiss (0.4.0)
+    jekyll-theme-architect (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-cayman (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-dinky (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-hacker (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-leap-day (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-merlot (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-midnight (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-minimal (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-modernist (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-primer (0.2.1)
+      jekyll (~> 3.3)
+    jekyll-theme-slate (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-tactile (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-theme-time-machine (0.0.4)
+      jekyll (~> 3.3)
+    jekyll-titles-from-headings (0.1.5)
+      jekyll (~> 3.3)
+    jekyll-watch (1.5.0)
+      listen (~> 3.0, < 3.1)
+    jemoji (0.8.0)
+      activesupport (~> 4.0)
+      gemoji (~> 3.0)
+      html-pipeline (~> 2.2)
+      jekyll (>= 3.0)
+    kramdown (1.13.2)
+    liquid (3.0.6)
+    listen (3.0.6)
+      rb-fsevent (>= 0.9.3)
+      rb-inotify (>= 0.9.7)
+    mercenary (0.3.6)
+    mini_portile2 (2.2.0)
+    minima (2.1.1)
+      jekyll (~> 3.3)
+    minitest (5.10.2)
+    multipart-post (2.0.0)
+    net-dns (0.8.0)
+    nokogiri (1.8.0)
+      mini_portile2 (~> 2.2.0)
+    octokit (4.7.0)
+      sawyer (~> 0.8.0, >= 0.5.3)
+    pathutil (0.14.0)
+      forwardable-extended (~> 2.6)
+    public_suffix (2.0.5)
+    rb-fsevent (0.9.8)
+    rb-inotify (0.9.10)
+      ffi (>= 0.5.0, < 2)
+    rouge (1.11.1)
+    safe_yaml (1.0.4)
+    sass (3.4.24)
+    sawyer (0.8.1)
+      addressable (>= 2.3.5, < 2.6)
+      faraday (~> 0.8, < 1.0)
+    terminal-table (1.8.0)
+      unicode-display_width (~> 1.1, >= 1.1.1)
+    thor (0.19.4)
+    thread_safe (0.3.6)
+    typhoeus (0.8.0)
+      ethon (>= 0.8.0)
+    tzinfo (1.2.3)
+      thread_safe (~> 0.1)
+    unicode-display_width (1.3.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  foreman
+  github-pages (= 140)
+
+BUNDLED WITH
+   1.15.1