Updating auth0.js URLs to use var instead of hard coded URL

Did not update /libraries/lock/v10/auth0js because already working on a branch that modifies this

Author: Jeff Smith

articles/_includes/_lock-sdk.html

@@ -106,7 +106,7 @@
 <label>Password</label><input type="password" id="password"><br>
 <button class="signin-db">Sign in with Email/Password</button>
 
-<script src="https://cdn.auth0.com/js/auth0/8.7/auth0.min.js"></script>
+<script src="${auth0js_urlv8}"></script>
 <script src="http://code.jquery.com/jquery.js"></script>
 <script>
   var webAuth = new auth0.WebAuth({

articles/client-auth/current/client-side-web.md

@@ -106,7 +106,7 @@ The [Auth0.js library](https://auth0.com/docs/libraries/auth0js) can assist you
         Log In
     </button>
   <script src="http://code.jquery.com/jquery-3.1.1.min.js" integrity="sha256-hVVnYaiADRTO2PzUGmuLJr8BLUSjGIZsDYGmIJLv2b8=" crossorigin="anonymous"></script>
-  <script src="https://cdn.auth0.com/js/auth0/8.7/auth0.min.js"></script>
+  <script src="${auth0js_urlv8}"></script>
   <script>
     (function () {
       var webAuth = new auth0.WebAuth({

articles/libraries/auth0js/v8/index.md

@@ -56,7 +56,6 @@ If you are using a bundler, you will want to install with `npm i auth0-js --prod
 Initialize a new instance of the Auth0 client as follows:
 
 ```html
-<script src="https://cdn.auth0.com/js/auth0/8.0.4/auth0.min.js"></script>
 <script type="text/javascript">
   var webAuth = new auth0.WebAuth({
     domain:       '${account.namespace}',

articles/libraries/auth0js/v8/migration-guide.md

@@ -42,7 +42,7 @@ You can find detailed information about supported methods in the [Auth0.js v8](/
 Initialization of auth0.js in your application will now use `auth0.WebAuth` instead of `Auth0`
 
 ```html
-<script src="https://cdn.auth0.com/js/auth0/8.1.0/auth0.min.js"></script>
+<script src="${auth0js_urlv8}"></script>
 <script type="text/javascript">
   var webAuth = new auth0.WebAuth({
     domain:       'YOUR_AUTH0_DOMAIN',