Bump jekyll to v3.9.0, kramdown to v2.3.0

lib/github-pages/dependencies.rb

@@ -7,11 +7,12 @@ module GitHubPages
   class Dependencies
     VERSIONS = {
       # Jekyll
-      "jekyll" => "3.8.7",
+      "jekyll" => "3.9.0",
       "jekyll-sass-converter" => "1.5.2",
 
       # Converters
-      "kramdown" => "1.17.0",
+      "kramdown" => "2.3.0",
+      "kramdown-parser-gfm" => "1.1.0",
       "jekyll-commonmark-ghpages" => "0.1.6",
 
       # Misc

spec/fixtures/kramdown-parser-gfm.md

@@ -0,0 +1,6 @@
+---
+---
+
+# Test
+
+~~Nope~~Yes

spec/fixtures/kramdown.md

@@ -2,3 +2,7 @@
 ---
 
 # Test
+
+### Math
+
+$$a^2 + b^2 = c^2$$

spec/github-pages/dependencies_spec.rb

@@ -4,7 +4,7 @@
 
 describe(GitHubPages::Dependencies) do
   CORE_DEPENDENCIES = %w(
-    jekyll kramdown liquid rouge jekyll-sass-converter
+    jekyll kramdown kramdown-parser-gfm liquid rouge jekyll-sass-converter
     github-pages-health-check
   ).freeze
   PLUGINS = described_class::VERSIONS.keys - CORE_DEPENDENCIES

spec/github-pages/integration_spec.rb

@@ -93,6 +93,16 @@ def rm_destination
       it "converts markdown to HTML" do
         expect(contents).to match('<h1 id="test">Test</h1>')
       end
+
+      it "converts math to mathjax" do
+        expect(contents).to include('\[a^2 + b^2 = c^2\]')
+      end
+    end
+
+    context "kramdown-parser-gfm" do
+      it "converts GFM to HTML" do
+        expect(contents).to match("<del>Nope</del>Yes")
+      end
     end
 
     context "liquid" do