docs(upgrade): escape script tags

closes #1584

Author: Foxandxss

public/docs/ts/latest/guide/upgrade.jade

@@ -96,7 +96,7 @@ include ../_util-fns
   up with a project structure with a large number of relatively small files. This is
   a much neater way to organize things than a small number of large files, but it
   doesn't work that well if you have to load all those files to the HTML page with
-  `<script>` tags. Especially when you also have to maintain those tags in the correct
+  &lt;script&gt; tags. Especially when you also have to maintain those tags in the correct
   order. That's why it's a good idea to start using a *module loader*.
 
   Using a module loader such as [SystemJS](https://github.com/systemjs/systemjs),
@@ -1171,7 +1171,7 @@ code-example(format="").
      version of the `Phone` Angular 2 service.
 
   Now that we are loading `phone.service.ts` through an import that is resolved
-  by SystemJS, we should **remove the `<script>` tag** for the service from `index.html`.
+  by SystemJS, we should **remove the &lt;script&gt; tag** for the service from `index.html`.
   This is something we'll do to all our components as we upgrade them. Simultaneously
   with the Angular 1 to 2 upgrade we're also migrating our code from scripts to modules.
 
@@ -1257,7 +1257,7 @@ code-example(format="").
   know that the return value of the downgrade method call will be something that can be
   used as a directive factory.
 
-  At this point, also remove the `<script>` tag for the phone list component from `index.html`.
+  At this point, also remove the &lt;script&gt; tag for the phone list component from `index.html`.
 
   Now we can start looking at our other component, which is the one for
   the phone details. Set the contents of `phone-detail.component.ts` as follows:
@@ -1314,7 +1314,7 @@ code-example(format="").
 +makeExample('upgrade-phonecat-2-hybrid/ts/app/main.ts', 'phone-detail', 'app/main.ts')
 
 :marked
-  We should now also remove the phone detail component `<script>` tag from `index.html`.
+  We should now also remove the phone detail component &lt;script&gt; tag from `index.html`.
 
   There's one additional step we need to take, which is to upgrade the
   `checkmark` filter that the template is using. We need an Angular 2
@@ -1330,7 +1330,7 @@ code-example(format="").
 
 :marked
   In the component we should now import and declare our newly created pipe (as well as
-  remove the filter `<script>` tag from `index.html`):
+  remove the filter &lt;script&gt; tag from `index.html`):
 
 +makeExample('upgrade-phonecat-2-hybrid/ts/app/phone-detail/phone-detail.component.ts', 'checkmark-pipe', 'app/phone-detail/phone-detail.component.ts')