fix: Gemfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-RUBY-NOKOGIRI-6056551
- https://snyk.io/vuln/SNYK-RUBY-NOKOGIRI-6056552
- https://snyk.io/vuln/SNYK-RUBY-NOKOGIRI-6056553
- https://snyk.io/vuln/SNYK-RUBY-NOKOGIRI-6056554
- https://snyk.io/vuln/SNYK-RUBY-NOKOGIRI-6056555

Gemfile

@@ -10,7 +10,7 @@ gem 'nanoc-redirector', '~> 0.2'
 gem 'nanoc-html-pipeline', '~> 0.3'
 gem 'gemoji', '2.1.0'
 gem 'html-pipeline-rouge_filter', '~> 1.0'
-gem 'extended-markdown-filter', '~> 0.4'
+gem 'extended-markdown-filter', '~> 0.7', '>= 0.7.0'
 gem 'html-pipeline-asciidoc_filter', '~> 1.5'
 gem 'github-markdown', '~> 0.6.9'
 gem 'kramdown'
@@ -23,5 +23,5 @@ gem 'pry-coolline'
 
 group :test do
   gem 'colorize', '~> 0.8.1'
-  gem 'html-proofer', '~> 3.7'
+  gem 'html-proofer', '~> 3.10', '>= 3.10.0'
 end