diff --git a/Gemfile.lock b/Gemfile.lock
index ff1e114..e940f48 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -18,7 +18,8 @@ GEM
     hamster (3.0.0)
       concurrent-ruby (~> 1.0)
     json_schema (0.19.1)
-    kramdown (1.17.0)
+    kramdown (2.3.1)
+      rexml
     nanoc (4.10.2)
       addressable (~> 2.5)
       cri (~> 2.15)
@@ -36,6 +37,7 @@ GEM
     rack (2.0.5)
     rake (12.3.1)
     ref (2.0.0)
+    rexml (3.2.4)
     slow_enumerator_tools (1.1.0)
     tomlrb (1.2.7)