[1.7.x] Fixed documentation of make_password kwargs.

Backport of ed7c4df1 from master

docs/topics/auth/passwords.txt

@@ -220,7 +220,7 @@ from the ``User`` model.
         to be an unusable password, resulting in this method returning
         ``False`` for such a password.
 
-.. function:: make_password(password[, salt, hashers])
+.. function:: make_password(password, salt=None, hasher='default')
 
     Creates a hashed password in the format used by this application. It takes
     one mandatory argument: the password in plain-text. Optionally, you can