diff --git a/Gemfile.lock b/Gemfile.lock
index 9c5a0cd..59b3cff 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -133,7 +133,7 @@ GEM
       thor (>= 0.18.1, < 2.0)
     rake (11.3.0)
     rchardet (1.8.0)
-    rdoc (5.0.0)
+    rdoc (6.3.1)
     rspec (3.5.0)
       rspec-core (~> 3.5.0)
       rspec-expectations (~> 3.5.0)