Bump nokogiri from 1.10.8 to 1.13.4

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.10.8 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@v1.10.8...v1.13.4)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -88,11 +88,12 @@ GEM
     mime-types (3.3.1)
       mime-types-data (~> 3.2015)
     mime-types-data (3.2019.1009)
-    mini_portile2 (2.4.0)
+    mini_portile2 (2.8.0)
     minitest (5.14.0)
     multi_json (1.14.1)
-    nokogiri (1.10.8)
-      mini_portile2 (~> 2.4.0)
+    nokogiri (1.13.4)
+      mini_portile2 (~> 2.8.0)
+      racc (~> 1.4)
     padrino-helpers (0.12.9)
       i18n (~> 0.6, >= 0.6.7)
       padrino-support (= 0.12.9)
@@ -101,6 +102,7 @@ GEM
       activesupport (>= 3.1)
     pygments.rb (1.2.1)
       multi_json (>= 1.0.0)
+    racc (1.6.0)
     rack (1.6.12)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)