ENYO-3946: Update platform detection for Silk 3.x

New versions of Fire OS use Silk 3.x, so detection code doesn't
understand their user agent strings.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Merge pull request #686 from enyojs/ENYO-3946-unwiredben

ENYO-3946: Update platform detection for Silk 3.x

Reviewed-By: Cole Davis (cole.davis@lge.com)