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