diff --git a/Gemfile b/Gemfile
index 6ac80f6..0d5549a 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,7 +1,7 @@
 source "https://rubygems.org"
 ruby RUBY_VERSION
 
-gem "jekyll", "3.4.3"
+gem "jekyll", "3.9.0"
 
 # to use GitHub Pages
 # gem "github-pages", group: :jekyll_plugins
diff --git a/Gemfile.lock b/Gemfile.lock
index c7cddcb..5575803 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,55 +1,71 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    addressable (2.5.1)
-      public_suffix (~> 2.0, >= 2.0.2)
+    addressable (2.8.2)
+      public_suffix (>= 2.0.2, < 6.0)
     colorator (1.1.0)
-    ffi (1.9.18)
+    concurrent-ruby (1.2.2)
+    em-websocket (0.5.3)
+      eventmachine (>= 0.12.9)
+      http_parser.rb (~> 0)
+    eventmachine (1.2.7)
+    ffi (1.15.5)
     forwardable-extended (2.6.0)
-    jekyll (3.4.3)
+    http_parser.rb (0.8.0)
+    i18n (0.9.5)
+      concurrent-ruby (~> 1.0)
+    jekyll (3.9.0)
       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)
-      liquid (~> 3.0)
+      jekyll-watch (~> 2.0)
+      kramdown (>= 1.17, < 3)
+      liquid (~> 4.0)
       mercenary (~> 0.3.3)
       pathutil (~> 0.9)
-      rouge (~> 1.7)
+      rouge (>= 1.7, < 4)
       safe_yaml (~> 1.0)
-    jekyll-feed (0.9.2)
-      jekyll (~> 3.3)
-    jekyll-redirect-from (0.12.1)
-      jekyll (~> 3.3)
-    jekyll-sass-converter (1.5.0)
+    jekyll-feed (0.17.0)
+      jekyll (>= 3.7, < 5.0)
+    jekyll-redirect-from (0.16.0)
+      jekyll (>= 3.3, < 5.0)
+    jekyll-sass-converter (1.5.2)
       sass (~> 3.4)
-    jekyll-seo-tag (2.2.2)
-      jekyll (~> 3.3)
-    jekyll-sitemap (1.1.1)
-      jekyll (~> 3.3)
-    jekyll-watch (1.5.0)
-      listen (~> 3.0, < 3.1)
-    kramdown (1.13.2)
-    liquid (3.0.6)
-    listen (3.0.8)
-      rb-fsevent (~> 0.9, >= 0.9.4)
-      rb-inotify (~> 0.9, >= 0.9.7)
+    jekyll-seo-tag (2.8.0)
+      jekyll (>= 3.8, < 5.0)
+    jekyll-sitemap (1.4.0)
+      jekyll (>= 3.7, < 5.0)
+    jekyll-watch (2.2.1)
+      listen (~> 3.0)
+    kramdown (2.4.0)
+      rexml
+    liquid (4.0.4)
+    listen (3.8.0)
+      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 (0.9.8)
-    rb-inotify (0.9.8)
-      ffi (>= 0.5.0)
-    rouge (1.11.1)
-    safe_yaml (1.0.4)
-    sass (3.4.23)
+    public_suffix (5.0.1)
+    rb-fsevent (0.11.2)
+    rb-inotify (0.10.1)
+      ffi (~> 1.0)
+    rexml (3.2.5)
+    rouge (3.30.0)
+    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)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
-  jekyll (= 3.4.3)
+  jekyll (= 3.9.0)
   jekyll-feed
   jekyll-redirect-from
   jekyll-seo-tag
@@ -57,7 +73,7 @@ DEPENDENCIES
   tzinfo-data
 
 RUBY VERSION
-   ruby 2.3.1p112
+   ruby 2.7.6p219
 
 BUNDLED WITH
-   1.14.6
+   1.17.3