am 2c30fe8a: Doc change: fix typo in policy docs.

<p>

  At right is an example of an interstitial, modal ad that is displayed outside

  of the app. This is no a violation of policy.

  of the app. This is a violation of policy.

</p>

<h2 id="interfering" style="clear:right;">Interfering with Apps and Third-Party Ads</h2>