fix: Gemfile & Gemfile.lock to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-RUBY-NOKOGIRI-534637

Gemfile

@@ -1,5 +1,5 @@
 source "https://rubygems.org"
 
-gem 'github-pages', '>= 198'
-gem 'html-proofer', '>= 3.11.1'
+gem 'github-pages', '>= 201'
+gem 'html-proofer', '>= 3.13.0'
 gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw]

Gemfile.lock

@@ -27,10 +27,10 @@ GEM
     execjs (2.7.0)
     faraday (0.17.0)
       multipart-post (>= 1.2, < 3)
-    ffi (1.11.1)
+    ffi (1.11.2)
     forwardable-extended (2.6.0)
     gemoji (3.0.1)
-    github-pages (201)
+    github-pages (202)
       activesupport (= 4.2.11.1)
       github-pages-health-check (= 1.16.1)
       jekyll (= 3.8.5)
@@ -81,10 +81,10 @@ GEM
       octokit (~> 4.0)
       public_suffix (~> 3.0)
       typhoeus (~> 1.3)
-    html-pipeline (2.12.0)
+    html-pipeline (2.12.2)
       activesupport (>= 2)
       nokogiri (>= 1.4)
-    html-proofer (3.13.0)
+    html-proofer (3.14.1)
       addressable (~> 2.3)
       mercenary (~> 0.3)
       nokogiri (~> 1.10)
@@ -212,13 +212,13 @@ GEM
       jekyll (~> 3.5)
       jekyll-feed (~> 0.9)
       jekyll-seo-tag (~> 2.1)
-    minitest (5.12.2)
+    minitest (5.13.0)
     multipart-post (2.1.1)
-    nokogiri (1.10.4)
+    nokogiri (1.10.5)
       mini_portile2 (~> 2.4.0)
     octokit (4.14.0)
       sawyer (~> 0.8.0, >= 0.5.3)
-    parallel (1.18.0)
+    parallel (1.19.0)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
     public_suffix (3.1.1)
@@ -254,8 +254,8 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  github-pages (>= 198)
-  html-proofer (>= 3.11.1)
+  github-pages (>= 201)
+  html-proofer (>= 3.13.0)
   tzinfo-data
 
 BUNDLED WITH