docs(changelog): wrap jqLite example containing html with code block

This prevents the markdown parser from garbling the input and putting
out broken html.

Closes angular#11778
Fixes angular#11777
Fixes angular#11539

Author: Narretz

CHANGELOG.md

@@ -4877,7 +4877,7 @@ For more info: http://blog.angularjs.org/2013/12/angularjs-13-new-release-approa
   - properly toggle multiple classes
   ([4e73c80b](https://github.com/angular/angular.js/commit/4e73c80b17bd237a8491782bcf9e19f1889e12ed),
    [#4467](https://github.com/angular/angular.js/issues/4467), [#6448](https://github.com/angular/angular.js/issues/6448))
-  - make jqLite('<iframe src="someurl">').contents() return iframe document, as in jQuery
+  - make `jqLite(<iframe src="someurl">').contents()` return iframe document, as in jQuery
   ([05fbed57](https://github.com/angular/angular.js/commit/05fbed5710b702c111c1425a9e241c40d13b0a54),
    [#6320](https://github.com/angular/angular.js/issues/6320), [#6323](https://github.com/angular/angular.js/issues/6323))
 - **numberFilter:** convert all non-finite/non-numbers/non-numeric strings to the empty string