Minor grammatical fixes on warning message (#13654)

Author: benmurden

lib/elixir/lib/module/types/of.ex

@@ -678,8 +678,8 @@ defmodule Module.Types.Of do
 
           Comparison operators (>, <, >=, <=, min, and max) perform structural \
           and not semantic comparison. Comparing with a struct won't give meaningful \
-          results. Struct that can be compared typically define a compare/2 function \
-          within their modules that can be used for semantic comparison
+          results. Structs that can be compared typically define a compare/2 function \
+          within their modules that can be used for semantic comparison.
           """
         ])
     }

lib/elixir/test/elixir/module/types/expr_test.exs

@@ -382,7 +382,7 @@ defmodule Module.Types.ExprTest do
                     # from: types_test.ex:LINE-2
                     y = %Point{}
 
-                Comparison operators (>, <, >=, <=, min, and max) perform structural and not semantic comparison. Comparing with a struct won't give meaningful results. Struct that can be compared typically define a compare/2 function within their modules that can be used for semantic comparison
+                Comparison operators (>, <, >=, <=, min, and max) perform structural and not semantic comparison. Comparing with a struct won't give meaningful results. Structs that can be compared typically define a compare/2 function within their modules that can be used for semantic comparison.
                 """}
     end
   end