diff --git a/Gemfile.lock b/Gemfile.lock
index 25d72bc..0b27f47 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -13,11 +13,13 @@ GEM
     json (1.8.3)
     method_source (0.8.2)
     minitest (5.9.0)
+    nio4r (2.5.7)
     pry (0.10.3)
       coderay (~> 1.1.0)
       method_source (~> 0.8.1)
       slop (~> 3.4)
-    puma (3.4.0)
+    puma (4.3.8)
+      nio4r (~> 2.0)
     rack (1.6.4)
     rack-protection (1.5.3)
       rack