diff --git a/doc/Gemfile.lock b/doc/Gemfile.lock
index 69ec3469..3a469cc5 100644
--- a/doc/Gemfile.lock
+++ b/doc/Gemfile.lock
@@ -11,7 +11,9 @@ GEM
     asciidoctor-diagram-plantuml (1.2021.0)
     asciidoctor-kroki (0.4.0)
       asciidoctor (~> 2.0)
-    rexml (3.2.5)
+    rexml (3.3.3)
+      strscan
+    strscan (3.1.0)
 
 PLATFORMS
   x64-mingw32