Bump nokogiri from 1.10.4 to 1.10.8

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.10.4 to 1.10.8.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sparklemotion/nokogiri/compare/v1.10.4...v1.10.8)

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

Gemfile.lock

@@ -70,7 +70,7 @@ GEM
       cri (~> 2.3)
     naught (1.1.0)
     nenv (0.3.0)
-    nokogiri (1.10.4)
+    nokogiri (1.10.8)
       mini_portile2 (~> 2.4.0)
     notiffany (0.1.1)
       nenv (~> 0.1)
@@ -132,7 +132,7 @@ DEPENDENCIES
   feedjira (~> 2.0.0)
   guard-nanoc (~> 1.0.3)
   nanoc (~> 3.7.5)
-  nokogiri (~> 1.10.4)
+  nokogiri (~> 1.10.8)
   rdiscount (~> 2.1.8)
   ri_cal (~> 0.8.8)
   rqrcode_png (~> 0.1.5)