Update authentication plugin install instructions

Refs cakephp/authentication#692

Author: markstory

en/appendices/5-0-migration-guide.rst

@@ -47,8 +47,8 @@ Global
 Auth
 ----
 
-- `Auth` has been removed. Use the `cakephp/authentication <https://book.cakephp.org/authentication/2/en/index.html>`__ and
-  `cakephp/authorization <https://book.cakephp.org/authorization/2/en/index.html>`__ plugins instead.
+- `Auth` has been removed. Use the `cakephp/authentication <https://book.cakephp.org/authentication/3/en/index.html>`__ and
+  `cakephp/authorization <https://book.cakephp.org/authorization/3/en/index.html>`__ plugins instead.
 
 Cache
 -----

en/tutorials-and-examples/cms/authentication.rst

@@ -2,7 +2,7 @@ CMS Tutorial - Authentication
 #############################
 
 Now that our CMS has users, we can enable them to login using the
-`cakephp/authentication <https://book.cakephp.org/authentication/2>`__
+`cakephp/authentication <https://book.cakephp.org/authentication/>`__
 plugin. We'll start off by ensuring passwords are stored securely in
 our database. Then we are going to provide a working login and logout, and
 enable new users to register.
@@ -14,7 +14,7 @@ Use composer to install the Authentication Plugin:
 
 .. code-block:: console
 
-    composer require "cakephp/authentication:^3.0"
+    composer require "cakephp/authentication:~3.0"
 
 
 Adding Password Hashing