Fixing problem with some plugins showing up twice

The limiting parameter for Elastic Search is named `"from"` instead of `"start"`. As it is now the first 15 hits is fetched twice, for instance `amd-optimize` shows up twice in the result list.

I had the same problem with the Slush generator search page, see [Slush #8](https://github.com/slushjs/slush/issues/8).

This pull request fixes that.