Bump jekyll from 3.8.7 to 3.9.0

Bumps [jekyll](https://github.com/jekyll/jekyll) from 3.8.7 to 3.9.0.
- [Release notes](https://github.com/jekyll/jekyll/releases)
- [Changelog](https://github.com/jekyll/jekyll/blob/master/History.markdown)
- [Commits](jekyll/jekyll@v3.8.7...v3.9.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

Gemfile.lock

@@ -32,7 +32,7 @@ GEM
     coderay (1.1.3)
     colorator (1.1.0)
     colorize (0.8.1)
-    concurrent-ruby (1.1.6)
+    concurrent-ruby (1.1.7)
     diff-lcs (1.4.2)
     docile (1.1.5)
     domain_name (0.5.20190701)
@@ -64,14 +64,14 @@ GEM
     i18n (0.9.5)
       concurrent-ruby (~> 1.0)
     io-like (0.3.1)
-    jekyll (3.8.7)
+    jekyll (3.9.0)
       addressable (~> 2.4)
       colorator (~> 1.0)
       em-websocket (~> 0.5)
       i18n (~> 0.7)
       jekyll-sass-converter (~> 1.0)
       jekyll-watch (~> 2.0)
-      kramdown (~> 1.14)
+      kramdown (>= 1.17, < 3)
       liquid (~> 4.0)
       mercenary (~> 0.3.3)
       pathutil (~> 0.9)
@@ -108,7 +108,8 @@ GEM
       html-pipeline (~> 2.2)
       jekyll (>= 3.0, < 5.0)
     json (2.3.0)
-    kramdown (1.17.0)
+    kramdown (2.3.0)
+      rexml
     liquid (4.0.3)
     listen (3.2.1)
       rb-fsevent (~> 0.10, >= 0.10.3)
@@ -150,7 +151,7 @@ GEM
       mime-types (>= 1.16, < 4.0)
       netrc (~> 0.8)
     rexml (3.2.4)
-    rouge (3.20.0)
+    rouge (3.21.0)
     rspec (3.9.0)
       rspec-core (~> 3.9.0)
       rspec-expectations (~> 3.9.0)