diff --git a/Gemfile.lock b/Gemfile.lock
index a2199bb..c305633 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -150,7 +150,8 @@ GEM
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
     public_suffix (3.1.1)
-    puma (3.12.1)
+    puma (4.0.1)
+      nio4r (~> 2.0)
     rack (2.0.7)
     rack-proxy (0.6.5)
       rack