Update to commonmarker gem v0.21

Gemfile

@@ -149,7 +149,7 @@ gem 'html-pipeline', '~> 2.12'
 gem 'deckar01-task_list', '2.3.1'
 gem 'gitlab-markup', '~> 1.7.1'
 gem 'github-markup', '~> 1.7.0', require: 'github/markup'
-gem 'commonmarker', '~> 0.20'
+gem 'commonmarker', '~> 0.21'
 gem 'kramdown', '~> 2.3.0'
 gem 'RedCloth', '~> 4.3.2'
 gem 'rdoc', '~> 6.1.2'

Gemfile.lock

@@ -177,7 +177,7 @@ GEM
       open4 (~> 1.3)
     coderay (1.1.3)
     colored2 (3.1.2)
-    commonmarker (0.20.1)
+    commonmarker (0.21.0)
       ruby-enum (~> 0.5)
     concord (0.1.5)
       adamantium (~> 0.2.0)
@@ -1041,7 +1041,7 @@ GEM
     rubocop-rspec (1.44.1)
       rubocop (~> 0.87)
       rubocop-ast (>= 0.7.1)
-    ruby-enum (0.7.2)
+    ruby-enum (0.8.0)
       i18n
     ruby-fogbugz (0.2.1)
       crack (~> 0.4)
@@ -1292,7 +1292,7 @@ DEPENDENCIES
   capybara-screenshot (~> 1.0.22)
   carrierwave (~> 1.3)
   charlock_holmes (~> 0.7.7)
-  commonmarker (~> 0.20)
+  commonmarker (~> 0.21)
   concurrent-ruby (~> 1.1)
   connection_pool (~> 2.0)
   countries (~> 3.0)