diff --git a/Gemfile.lock b/Gemfile.lock
index 3d2cd6c6..d70565db 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -134,7 +134,7 @@ GEM
     mini_portile2 (2.8.5)
     minitest (5.20.0)
     msgpack (1.7.2)
-    mutex_m (0.1.2)
+    mutex_m (0.2.0)
     net-imap (0.4.4)
       date
       net-protocol