Bump nokogiri from 1.8.1 to 1.13.4

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.8.1 to 1.13.4.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/v1.13.4/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.8.1...v1.13.4)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Gemfile.lock

@@ -36,12 +36,13 @@ GEM
       nokogiri (>= 1.5.9)
     metaclass (0.0.4)
     method_source (0.9.0)
-    mini_portile2 (2.3.0)
+    mini_portile2 (2.8.0)
     minitest (5.10.3)
     mocha (1.2.1)
       metaclass (~> 0.0.1)
-    nokogiri (1.8.1)
-      mini_portile2 (~> 2.3.0)
+    nokogiri (1.13.4)
+      mini_portile2 (~> 2.8.0)
+      racc (~> 1.4)
     parser (2.6.3.0)
       ast (~> 2.4.0)
     pry (0.11.2)
@@ -50,6 +51,7 @@ GEM
     pry-byebug (3.5.0)
       byebug (~> 9.1)
       pry (~> 0.10)
+    racc (1.6.0)
     rails-dom-testing (2.0.3)
       activesupport (>= 4.2.0)
       nokogiri (>= 1.6)