docs(chore): make styles consistent for API doc headings

Closes #4816

modules/angular2/src/router/path_location_strategy.ts

@@ -20,7 +20,7 @@ import {LocationStrategy, normalizeQueryParams} from './location_strategy';
  * `location.go('/foo')`, the browser's URL will become
  * `example.com/my/app/foo`.
  *
- * ## Example
+ * ### Example
  *
  * ```
  * import {Component, provide} from 'angular2/angular2';