Mention rack 2.1.0 support in UPGRADING.md (#2130)

maxkerp · web-flow · commit 613f9f1c9881 · 2021-05-05T09:42:23.000-04:00
diff --git a/UPGRADING.md b/UPGRADING.md
@@ -216,6 +216,8 @@ end
 
 ### Upgrading to >= 1.3.0
 
+You will need to upgrade to this version if you depend on `rack >= 2.1.0`.
+
 #### Ruby
 
 After adding dry-types, Ruby 2.4 or newer is required.
