diff --git a/Gemfile.lock b/Gemfile.lock
index 73a69ed..444efd5 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -59,6 +59,7 @@ GEM
     minitest (5.11.3)
     minitest-rg (5.2.0)
       minitest (~> 5.0)
+    nio4r (2.5.8)
     parallel (1.17.0)
     parser (2.6.3.0)
       ast (~> 2.4.0)
@@ -66,7 +67,8 @@ GEM
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
     public_suffix (3.0.3)
-    puma (3.12.1)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     rack (2.0.7)
     rack-ssl-enforcer (0.2.9)
     rack-test (1.1.0)