diff --git a/Gemfile.lock b/Gemfile.lock
index f0dedcb..26947c8 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -170,7 +170,7 @@ GEM
     mocha (2.1.0)
       ruby2_keywords (>= 0.0.5)
     msgpack (1.7.2)
-    mutex_m (0.1.2)
+    mutex_m (0.2.0)
     net-imap (0.4.3)
       date
       net-protocol