Fix for CVE-2019-5477

https://nvd.nist.gov/vuln/detail/CVE-2019-5477

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/docs/Gemfile.lock b/docs/Gemfile.lock
index 1bf905d..f67b03f 100644
--- a/docs/Gemfile.lock
+++ b/docs/Gemfile.lock
@@ -205,7 +205,7 @@
       jekyll-seo-tag (~> 2.1)
     minitest (5.11.3)
     multipart-post (2.0.0)
-    nokogiri (1.9.1)
+    nokogiri (1.10.4)
       mini_portile2 (~> 2.4.0)
     octokit (4.13.0)
       sawyer (~> 0.8.0, >= 0.5.3)