diff --git a/Gemfile.lock b/Gemfile.lock
index ccd1ffc..35e6fa2 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -11,7 +11,7 @@ GEM
       citeproc (~> 1.0, >= 1.0.9)
       csl (~> 1.5)
     colorator (1.1.0)
-    concurrent-ruby (1.1.5)
+    concurrent-ruby (1.3.7)
     csl (1.5.0)
       namae (~> 1.0)
     csl-styles (1.0.1.9)