Bump gem versions to silence security warning.

docs/Gemfile

@@ -2,4 +2,4 @@
 
 source "https://rubygems.org"
 
-gem "github-pages", "~> 206"
+gem "github-pages", "~> 207"

docs/Gemfile.lock

@@ -1,12 +1,11 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    activesupport (6.0.3.1)
+    activesupport (5.2.4.3)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
       tzinfo (~> 1.1)
-      zeitwerk (~> 2.2, >= 2.2.2)
     addressable (2.7.0)
       public_suffix (>= 2.0.2, < 5.0)
     coffee-script (2.4.1)
@@ -16,9 +15,9 @@ GEM
     colorator (1.1.0)
     commonmarker (0.17.13)
       ruby-enum (~> 0.5)
-    concurrent-ruby (1.1.6)
-    dnsruby (1.61.3)
-      addressable (~> 2.5)
+    concurrent-ruby (1.1.7)
+    dnsruby (1.61.4)
+      simpleidn (~> 0.1)
     em-websocket (0.5.1)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.6.0)
@@ -28,12 +27,12 @@ GEM
     execjs (2.7.0)
     faraday (1.0.1)
       multipart-post (>= 1.2, < 3)
-    ffi (1.12.2)
+    ffi (1.13.1)
     forwardable-extended (2.6.0)
     gemoji (3.0.1)
-    github-pages (206)
+    github-pages (207)
       github-pages-health-check (= 1.16.1)
-      jekyll (= 3.8.7)
+      jekyll (= 3.9.0)
       jekyll-avatar (= 0.7.0)
       jekyll-coffeescript (= 1.1.1)
       jekyll-commonmark-ghpages (= 0.1.6)
@@ -67,7 +66,8 @@ GEM
       jekyll-theme-time-machine (= 0.1.1)
       jekyll-titles-from-headings (= 0.5.3)
       jemoji (= 0.11.1)
-      kramdown (= 1.17.0)
+      kramdown (= 2.3.0)
+      kramdown-parser-gfm (= 1.1.0)
       liquid (= 4.0.3)
       mercenary (~> 0.3)
       minima (= 2.5.1)
@@ -80,20 +80,20 @@ GEM
       octokit (~> 4.0)
       public_suffix (~> 3.0)
       typhoeus (~> 1.3)
-    html-pipeline (2.12.3)
+    html-pipeline (2.14.0)
       activesupport (>= 2)
       nokogiri (>= 1.4)
     http_parser.rb (0.6.0)
     i18n (0.9.5)
       concurrent-ruby (~> 1.0)
-    jekyll (3.8.7)
+    jekyll (3.9.0)
       addressable (~> 2.4)
       colorator (~> 1.0)
       em-websocket (~> 0.5)
       i18n (~> 0.7)
       jekyll-sass-converter (~> 1.0)
       jekyll-watch (~> 2.0)
-      kramdown (~> 1.14)
+      kramdown (>= 1.17, < 3)
       liquid (~> 4.0)
       mercenary (~> 0.3.3)
       pathutil (~> 0.9)
@@ -191,7 +191,10 @@ GEM
       gemoji (~> 3.0)
       html-pipeline (~> 2.2)
       jekyll (>= 3.0, < 5.0)
-    kramdown (1.17.0)
+    kramdown (2.3.0)
+      rexml
+    kramdown-parser-gfm (1.1.0)
+      kramdown (~> 2.0)
     liquid (4.0.3)
     listen (3.2.1)
       rb-fsevent (~> 0.10, >= 0.10.3)
@@ -204,7 +207,7 @@ GEM
       jekyll-seo-tag (~> 2.1)
     minitest (5.14.1)
     multipart-post (2.1.1)
-    nokogiri (1.10.9)
+    nokogiri (1.10.10)
       mini_portile2 (~> 2.4.0)
     octokit (4.18.0)
       faraday (>= 0.9)
@@ -215,10 +218,11 @@ GEM
     rb-fsevent (0.10.4)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
+    rexml (3.2.4)
     rouge (3.19.0)
     ruby-enum (0.8.0)
       i18n
-    rubyzip (2.3.0)
+    rubyzip (1.3.0)
     safe_yaml (1.0.5)
     sass (3.7.4)
       sass-listen (~> 4.0.0)
@@ -228,21 +232,25 @@ GEM
     sawyer (0.8.2)
       addressable (>= 2.3.5)
       faraday (> 0.8, < 2.0)
+    simpleidn (0.1.1)
+      unf (~> 0.1.4)
     terminal-table (1.8.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
     thread_safe (0.3.6)
     typhoeus (1.4.0)
       ethon (>= 0.9.0)
     tzinfo (1.2.7)
       thread_safe (~> 0.1)
+    unf (0.1.4)
+      unf_ext
+    unf_ext (0.0.7.7)
     unicode-display_width (1.7.0)
-    zeitwerk (2.3.0)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
-  github-pages (~> 206)
+  github-pages (~> 207)
 
 BUNDLED WITH
    2.1.4