Bump nokogiri from 1.6.5 to 1.9.1 in /brooklyn-docs

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.6.5 to 1.9.1.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](https://github.com/sparklemotion/nokogiri/compare/v1.6.5...v1.9.1)

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

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/brooklyn-docs/Gemfile.lock b/brooklyn-docs/Gemfile.lock
index f48dc2b..a9b3be8 100644
--- a/brooklyn-docs/Gemfile.lock
+++ b/brooklyn-docs/Gemfile.lock
@@ -59,9 +59,9 @@
       rb-fsevent (>= 0.9.3)
       rb-inotify (>= 0.9)
     mercenary (0.3.5)
-    mini_portile (0.6.2)
-    nokogiri (1.6.5)
-      mini_portile (~> 0.6.0)
+    mini_portile2 (2.4.0)
+    nokogiri (1.9.1)
+      mini_portile2 (~> 2.4.0)
     parallel (1.3.3)
     parslet (1.5.0)
       blankslate (~> 2.0)