Update videojs-contrib-ads to 0.4.0

We are having a discussion in https://github.com/videojs/videojs-contrib-ads/pull/43 about whether `contentupdate` should fire when the ads plugin finishes initialization. I'm feeling like the name of the event implies that the video source has *changed* and so it's a little strange for it to fire if contrib-ads is initialized with a video element statically configured with a src URL. @nhjm449 noted this project was relying on the previous behavior so I wanted to find out how disruptive this change would be. What do you guys think?

##### Changes in this patch
Pull in the latest version of videojs-contrib-ads. Trigger an ads request during plugin initiatlization if there is already content in the player. Add grunt-connect as a dev dependency to make it a tiny bit easier to load up the example page over HTTP.