fix: Gemfile & Gemfile.lock to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-RUBY-REXML-6861566

Gemfile

@@ -7,15 +7,15 @@ source "https://rubygems.org"
 #
 # This will help ensure the proper Jekyll version is running.
 # Happy Jekylling!
-gem "jekyll", "~> 4.2.0"
+gem "jekyll", "~> 4.2.1"
 # This is the default theme for new Jekyll sites. You may change this to anything you like.
 gem "minima", "~> 2.5"
 # If you want to use GitHub Pages, remove the "gem "jekyll"" above and
 # uncomment the line below. To upgrade, run `bundle update github-pages`.
 # gem "github-pages", group: :jekyll_plugins
 # If you have any plugins, put them here!
 group :jekyll_plugins do
-  gem "jekyll-feed", "~> 0.12"
+  gem "jekyll-feed", "~> 0.16", ">= 0.16.0"
 end
 
 # Windows and JRuby does not include zoneinfo files, so bundle the tzinfo-data gem

Gemfile.lock

@@ -1,20 +1,20 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    addressable (2.8.0)
-      public_suffix (>= 2.0.2, < 5.0)
+    addressable (2.8.6)
+      public_suffix (>= 2.0.2, < 6.0)
     colorator (1.1.0)
-    concurrent-ruby (1.1.9)
-    em-websocket (0.5.2)
+    concurrent-ruby (1.2.3)
+    em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
-      http_parser.rb (~> 0.6.0)
+      http_parser.rb (~> 0)
     eventmachine (1.2.7)
-    ffi (1.15.3)
+    ffi (1.16.3)
     forwardable-extended (2.6.0)
-    http_parser.rb (0.6.0)
-    i18n (1.8.10)
+    http_parser.rb (0.8.0)
+    i18n (1.14.5)
       concurrent-ruby (~> 1.0)
-    jekyll (4.2.0)
+    jekyll (4.2.2)
       addressable (~> 2.4)
       colorator (~> 1.0)
       em-websocket (~> 0.5)
@@ -29,20 +29,20 @@ GEM
       rouge (~> 3.0)
       safe_yaml (~> 1.0)
       terminal-table (~> 2.0)
-    jekyll-feed (0.15.1)
+    jekyll-feed (0.17.0)
       jekyll (>= 3.7, < 5.0)
-    jekyll-sass-converter (2.1.0)
+    jekyll-sass-converter (2.2.0)
       sassc (> 2.0.1, < 3.0)
     jekyll-seo-tag (2.7.1)
       jekyll (>= 3.8, < 5.0)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
-    kramdown (2.3.1)
+    kramdown (2.4.0)
       rexml
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
-    liquid (4.0.3)
-    listen (3.7.0)
+    liquid (4.0.4)
+    listen (3.9.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     mercenary (0.4.0)
@@ -52,31 +52,34 @@ GEM
       jekyll-seo-tag (~> 2.1)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
-    public_suffix (4.0.6)
-    rb-fsevent (0.11.0)
+    public_suffix (5.0.5)
+    rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.5)
-    rouge (3.26.0)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
+    rouge (3.30.0)
     safe_yaml (1.0.5)
     sassc (2.4.0)
       ffi (~> 1.9)
+    strscan (3.1.0)
     terminal-table (2.0.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
-    unicode-display_width (1.7.0)
+    unicode-display_width (1.8.0)
 
 PLATFORMS
+  ruby
   universal-darwin-20
   x86_64-darwin-18
   x86_64-linux
 
 DEPENDENCIES
-  jekyll (~> 4.2.0)
-  jekyll-feed (~> 0.12)
+  jekyll (~> 4.2.1)
+  jekyll-feed (~> 0.16, >= 0.16.0)
   minima (~> 2.5)
   tzinfo (~> 1.2)
   tzinfo-data
   wdm (~> 0.1.1)
 
 BUNDLED WITH
-   2.2.26
+   2.1.4