Update devDependencies and gems.

Gemfile

@@ -3,7 +3,7 @@ source 'https://rubygems.org'
 group :development, :test do
   gem 'jekyll', '~> 3.8.6'
   gem 'jekyll-redirect-from', '~> 0.15.0'
-  gem 'jekyll-sitemap', '~> 1.3.1'
+  gem 'jekyll-sitemap', '~> 1.4.0'
   gem 'jekyll-toc', '~> 0.11.0'
   gem 'wdm', '~> 0.1.1', :install_if => Gem.win_platform?
 end

Gemfile.lock

@@ -10,8 +10,8 @@ GEM
       http_parser.rb (~> 0.6.0)
     eventmachine (1.2.7)
     eventmachine (1.2.7-x64-mingw32)
-    ffi (1.11.1)
-    ffi (1.11.1-x64-mingw32)
+    ffi (1.11.2)
+    ffi (1.11.2-x64-mingw32)
     forwardable-extended (2.6.0)
     http_parser.rb (0.6.0)
     i18n (0.9.5)
@@ -33,7 +33,7 @@ GEM
       jekyll (>= 3.3, < 5.0)
     jekyll-sass-converter (1.5.2)
       sass (~> 3.4)
-    jekyll-sitemap (1.3.1)
+    jekyll-sitemap (1.4.0)
       jekyll (>= 3.7, < 5.0)
     jekyll-toc (0.11.0)
       nokogiri (~> 1.9)
@@ -56,7 +56,7 @@ GEM
     rb-fsevent (0.10.3)
     rb-inotify (0.10.0)
       ffi (~> 1.0)
-    rouge (3.12.0)
+    rouge (3.13.0)
     safe_yaml (1.0.5)
     sass (3.7.4)
       sass-listen (~> 4.0.0)
@@ -72,7 +72,7 @@ PLATFORMS
 DEPENDENCIES
   jekyll (~> 3.8.6)
   jekyll-redirect-from (~> 0.15.0)
-  jekyll-sitemap (~> 1.3.1)
+  jekyll-sitemap (~> 1.4.0)
   jekyll-toc (~> 0.11.0)
   wdm (~> 0.1.1)