Possible typo in Feed constructor

[Ian Shehadeh]

I've just run into an error this.emit is not a function, which occured when both eagerUpdate and sparse are enabled. I'm pretty sure that's due to this line, https://github.com/mafintosh/hypercore/blob/c5cec3badbcfb864dd7ccf6fb38350ff10deb360/index.js#L127 It looks like this is pointing to the loop function, instead of the Feed.