Updating USAGE information for Mailer generator [#3801 status:resolved]

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

railties/lib/generators/rails/mailer/USAGE

@@ -2,7 +2,7 @@ Description:
     Stubs out a new mailer and its views. Pass the mailer name, either
     CamelCased or under_scored, and an optional list of emails as arguments.
 
-    This generates a mailer class in app/models and invokes your template
+    This generates a mailer class in app/mailers and invokes your template
     engine and test framework generators.
 
 Example: