use peerDependencies for baconjs

hi!

[peerDependencies](http://blog.nodejs.org/2013/02/07/peer-dependencies/) help when multiple plugins want to play together. without peerDeps, it's likely each plugin would have it's own `Bacon` instance, which [is bad](https://github.com/baconjs/bacon.js/issues/296).

also, i'd recommend a looser peerDep value (like `0.7.x`), but `0.7.6` (upgraded from `0.7.5-alpha-1`) is doable.

cheers :)