diff --git a/Gemfile.lock b/Gemfile.lock
index 70bce5b..6328e02 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -15,11 +15,11 @@ GEM
     hashdiff (1.0.1)
     libxml-ruby (3.2.2)
     power_assert (2.0.1)
-    psych (4.0.3)
+    psych (5.1.2)
       stringio
     public_suffix (4.0.6)
     rake (13.0.6)
-    rdoc (6.4.0)
+    rdoc (6.4.1.1)
       psych (>= 4.0.0)
     rexml (3.2.5)
     simplecov (0.21.2)
@@ -28,7 +28,7 @@ GEM
       simplecov_json_formatter (~> 0.1)
     simplecov-html (0.12.3)
     simplecov_json_formatter (0.1.4)
-    stringio (3.0.1)
+    stringio (3.1.0)
     test-unit (3.5.3)
       power_assert
     vcr (3.0.3)