diff --git a/Gemfile.lock b/Gemfile.lock
index a424fa7..f3e403e 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -69,7 +69,8 @@ GEM
     json_schema (0.20.6)
     katex (0.5.1)
       execjs (~> 2.7)
-    kramdown (2.1.0)
+    kramdown (2.3.1)
+      rexml
     kramdown-math-sskatex (1.0.0)
       kramdown (~> 2.0)
       sskatex (>= 0.9.37)
@@ -128,6 +129,7 @@ GEM
       ffi (~> 1.0)
     rb-readline (0.5.5)
     ref (2.0.0)
+    rexml (3.2.4)
     ruby_dep (1.5.0)
     rubypants (0.7.0)
     sass (3.7.4)