Install missing dependency rake

Gemfile

@@ -8,6 +8,7 @@ gem 'rouge', '~> 3.25.0'
 gem 'jekyll-redirect-from', '~> 0.16.0'
 gem 'jekyll-feed', '~> 0.15.1'
 gem "jekyll-sitemap", "~> 1.4"
+gem "rake", "~> 13.0"
 
 group :test do
     gem 'html-proofer', '~> 3.18.5'

Gemfile.lock

@@ -69,6 +69,7 @@ GEM
       forwardable-extended (~> 2.6)
     public_suffix (4.0.6)
     rainbow (3.0.0)
+    rake (13.0.3)
     rb-fsevent (0.10.4)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
@@ -95,6 +96,7 @@ DEPENDENCIES
   jekyll-paginate (~> 1.1.0)
   jekyll-redirect-from (~> 0.16.0)
   jekyll-sitemap (~> 1.4)
+  rake (~> 13.0)
   rouge (~> 3.25.0)
   yaml-lint (~> 0.0.7)