Update Gemfile (#3980)

Author: M-i-k-e-l

Gemfile.lock

@@ -64,7 +64,7 @@ GEM
       netrc (~> 0.11)
     cocoapods-try (1.2.0)
     colored2 (3.1.2)
-    concurrent-ruby (1.2.2)
+    concurrent-ruby (1.3.3)
     connection_pool (2.5.5)
     drb (2.2.3)
     escape (0.0.4)