docs($sce): fix typo.

Closes angular#6882

src/ng/sce.js

@@ -522,7 +522,7 @@ function $SceDelegateProvider() {
  * | `$sce.HTML`         | For HTML that's safe to source into the application.  The {@link ng.directive:ngBindHtml ngBindHtml} directive uses this context for bindings. |
  * | `$sce.CSS`          | For CSS that's safe to source into the application.  Currently unused.  Feel free to use it in your own directives. |
  * | `$sce.URL`          | For URLs that are safe to follow as links.  Currently unused (`<a href=` and `<img src=` sanitize their urls and don't constitute an SCE context. |
- * | `$sce.RESOURCE_URL` | For URLs that are not only safe to follow as links, but whose contens are also safe to include in your application.  Examples include `ng-include`, `src` / `ngSrc` bindings for tags other than `IMG` (e.g. `IFRAME`, `OBJECT`, etc.)  <br><br>Note that `$sce.RESOURCE_URL` makes a stronger statement about the URL than `$sce.URL` does and therefore contexts requiring values trusted for `$sce.RESOURCE_URL` can be used anywhere that values trusted for `$sce.URL` are required. |
+ * | `$sce.RESOURCE_URL` | For URLs that are not only safe to follow as links, but whose contents are also safe to include in your application.  Examples include `ng-include`, `src` / `ngSrc` bindings for tags other than `IMG` (e.g. `IFRAME`, `OBJECT`, etc.)  <br><br>Note that `$sce.RESOURCE_URL` makes a stronger statement about the URL than `$sce.URL` does and therefore contexts requiring values trusted for `$sce.RESOURCE_URL` can be used anywhere that values trusted for `$sce.URL` are required. |
  * | `$sce.JS`           | For JavaScript that is safe to execute in your application's context.  Currently unused.  Feel free to use it in your own directives. |
  *
  * ## Format of items in {@link ng.$sceDelegateProvider#resourceUrlWhitelist resourceUrlWhitelist}/{@link ng.$sceDelegateProvider#resourceUrlBlacklist Blacklist} <a name="resourceUrlPatternItem"></a>