Update gem

Gemfile.lock

 GEM
   remote: http://rubygems.org/
   specs:
-    addressable (2.6.0)
-      public_suffix (>= 2.0.2, < 4.0)
+    addressable (2.7.0)
+      public_suffix (>= 2.0.2, < 5.0)
     colorator (1.1.0)
-    concurrent-ruby (1.1.4)
+    concurrent-ruby (1.1.6)
     em-websocket (0.5.1)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.6.0)
     eventmachine (1.2.7)
-    ffi (1.10.0)
+    ffi (1.12.2)
     forwardable-extended (2.6.0)
     http_parser.rb (0.6.0)
-    i18n (0.9.5)
+    i18n (1.8.2)
       concurrent-ruby (~> 1.0)
-    jekyll (3.8.5)
+    jekyll (4.0.0)
       addressable (~> 2.4)
       colorator (~> 1.0)
       em-websocket (~> 0.5)
-      i18n (~> 0.7)
-      jekyll-sass-converter (~> 1.0)
+      i18n (>= 0.9.5, < 2)
+      jekyll-sass-converter (~> 2.0)
       jekyll-watch (~> 2.0)
-      kramdown (~> 1.14)
+      kramdown (~> 2.1)
+      kramdown-parser-gfm (~> 1.0)
       liquid (~> 4.0)
       mercenary (~> 0.3.3)
       pathutil (~> 0.9)
-      rouge (>= 1.7, < 4)
+      rouge (~> 3.0)
       safe_yaml (~> 1.0)
+      terminal-table (~> 1.8)
     jekyll-paginate (1.1.0)
-    jekyll-sass-converter (1.5.2)
-      sass (~> 3.4)
-    jekyll-sitemap (1.3.1)
+    jekyll-sass-converter (2.1.0)
+      sassc (> 2.0.1, < 3.0)
+    jekyll-sitemap (1.4.0)
       jekyll (>= 3.7, < 5.0)
-    jekyll-watch (2.1.2)
+    jekyll-watch (2.2.1)
       listen (~> 3.0)
-    kramdown (1.17.0)
-    liquid (4.0.1)
-    listen (3.1.5)
-      rb-fsevent (~> 0.9, >= 0.9.4)
-      rb-inotify (~> 0.9, >= 0.9.7)
-      ruby_dep (~> 1.2)
+    kramdown (2.1.0)
+    kramdown-parser-gfm (1.1.0)
+      kramdown (~> 2.0)
+    liquid (4.0.3)
+    listen (3.2.1)
+      rb-fsevent (~> 0.10, >= 0.10.3)
+      rb-inotify (~> 0.9, >= 0.9.10)
     mercenary (0.3.6)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
-    public_suffix (3.0.3)
+    public_suffix (4.0.4)
     rb-fsevent (0.10.3)
-    rb-inotify (0.10.0)
+    rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rouge (3.3.0)
-    ruby_dep (1.5.0)
-    safe_yaml (1.0.4)
-    sass (3.7.3)
+    rouge (3.17.0)
+    safe_yaml (1.0.5)
+    sass (3.7.4)
       sass-listen (~> 4.0.0)
     sass-listen (4.0.0)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
+    sassc (2.2.1)
+      ffi (~> 1.9)
     support-for (1.0.7)
       sass (~> 3.3)
+    terminal-table (1.8.0)
+      unicode-display_width (~> 1.1, >= 1.1.1)
+    unicode-display_width (1.7.0)
 
 PLATFORMS
   ruby
@@ -68,4 +75,4 @@ DEPENDENCIES
   support-for
 
 BUNDLED WITH
-   2.0.2
+   2.1.4