Merge pull request #18190 from ef718/master

Fix grammar in Caching with Rails docs

guides/source/caching_with_rails.md

@@ -107,7 +107,7 @@ This method generates a cache key that depends on all products and can be used i
 <% end %>
 ```
 
-If you want to cache a fragment under certain condition you can use `cache_if` or `cache_unless`
+If you want to cache a fragment under certain conditions, you can use `cache_if` or `cache_unless`
 
 ```erb
 <% cache_if (condition, cache_key_for_products) do %>