Bump jekyll version to 3.8.6

Gemfile.lock

 GEM
   remote: https://rubygems.org/
   specs:
-    addressable (2.5.1)
-      public_suffix (~> 2.0, >= 2.0.2)
+    addressable (2.7.0)
+      public_suffix (>= 2.0.2, < 5.0)
     builder (3.2.3)
     colorator (1.1.0)
-    ffi (1.9.18)
+    concurrent-ruby (1.1.5)
+    em-websocket (0.5.1)
+      eventmachine (>= 0.12.9)
+      http_parser.rb (~> 0.6.0)
+    eventmachine (1.2.7)
+    ffi (1.11.3)
     forwardable-extended (2.6.0)
-    jekyll (3.5.2)
+    http_parser.rb (0.6.0)
+    i18n (0.9.5)
+      concurrent-ruby (~> 1.0)
+    jekyll (3.8.6)
       addressable (~> 2.4)
       colorator (~> 1.0)
+      em-websocket (~> 0.5)
+      i18n (~> 0.7)
       jekyll-sass-converter (~> 1.0)
-      jekyll-watch (~> 1.1)
-      kramdown (~> 1.3)
+      jekyll-watch (~> 2.0)
+      kramdown (~> 1.14)
       liquid (~> 4.0)
       mercenary (~> 0.3.3)
       pathutil (~> 0.9)
-      rouge (~> 1.7)
+      rouge (>= 1.7, < 4)
       safe_yaml (~> 1.0)
     jekyll-multiple-languages-plugin (1.5.1)
       jekyll (>= 2.0, < 4.0)
     jekyll-paginate (1.1.0)
-    jekyll-sass-converter (1.5.0)
+    jekyll-sass-converter (1.5.2)
       sass (~> 3.4)
-    jekyll-watch (1.5.0)
-      listen (~> 3.0, < 3.1)
-    kramdown (1.14.0)
-    liquid (4.0.0)
-    listen (3.0.8)
-      rb-fsevent (~> 0.9, >= 0.9.4)
-      rb-inotify (~> 0.9, >= 0.9.7)
+    jekyll-watch (2.2.1)
+      listen (~> 3.0)
+    kramdown (1.17.0)
+    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 (0.14.0)
+    pathutil (0.16.2)
       forwardable-extended (~> 2.6)
-    public_suffix (2.0.5)
-    rb-fsevent (0.10.2)
-    rb-inotify (0.9.10)
-      ffi (>= 0.5.0, < 2)
-    rouge (1.11.1)
+    public_suffix (4.0.1)
+    rb-fsevent (0.10.3)
+    rb-inotify (0.10.0)
+      ffi (~> 1.0)
+    rouge (3.14.0)
     rubysl-rexml (2.0.4)
-    safe_yaml (1.0.4)
-    sass (3.5.1)
+    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)
@@ -57,4 +67,4 @@ DEPENDENCIES
   rubysl-rexml
 
 BUNDLED WITH
-   1.15.4
+   1.17.3