bower.json: switch from SteveSanderson/knockout to bowerjs/knockout
bower.json: switch from SteveSanderson/knockout to bowerjs/knockout

SteveSanderson/knockout (knockout) doesn't contain a compiled version
of knockout, so it's impossible to use with bower if you're not also
using grunt. bowerjs/knockout (knockout.js) has been updated
regularly, and allows for a broader range of build setups.

Signed-off-by: Evan Owen <a31932a4150a6c43f7c4879727da9a731c3d5877@gmail.com>

abradley2/knockback,npmcomponent/kmalakoff-knockback,kmalakoff/knockback,abradley2/knockback,kmalakoff/knockback