Fix amp-ad example to include amp-ad.js (#375)
Fix amp-ad example to include amp-ad.js (#375)

Fixes #364
ampproject/amp-by-example,camelburrito/amp-by-example,ampproject/amp-by-example,camelburrito/amp-by-example,ampproject/amp-by-example,ampproject/amp-by-example,camelburrito/amp-by-example,camelburrito/amp-by-example