Fix CVE-2019-16892

https://nvd.nist.gov/vuln/detail/CVE-2019-16892

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/docs/Gemfile.lock b/docs/Gemfile.lock
index f67b03f..0404271 100644
--- a/docs/Gemfile.lock
+++ b/docs/Gemfile.lock
@@ -219,7 +219,7 @@
     ruby-enum (0.7.2)
       i18n
     ruby_dep (1.5.0)
-    rubyzip (1.2.2)
+    rubyzip (2.0.0)
     safe_yaml (1.0.4)
     sass (3.7.2)
       sass-listen (~> 4.0.0)
@@ -244,6 +244,7 @@
 DEPENDENCIES
   github-pages
   jekyll (>= 3.7.4)
+  rubyzip (>= 1.3.0)
   tzinfo-data
 
 BUNDLED WITH