finagle-core: Add vkostyukov as owner
finagle-core: Add vkostyukov as owner

Problem / Solution

I've been contributing quite a while into Finagle's core I feel quite
comfortable (and ready!) beeing its owner.

RB_ID=881572

mkhq/finagle,koshelev/finagle,koshelev/finagle,koshelev/finagle,luciferous/finagle,twitter/finagle,luciferous/finagle,spockz/finagle,koshelev/finagle,mkhq/finagle,spockz/finagle,spockz/finagle,mkhq/finagle,mkhq/finagle,mkhq/finagle,twitter/finagle,mkhq/finagle,twitter/finagle,luciferous/finagle,koshelev/finagle,spockz/finagle,luciferous/finagle,twitter/finagle,koshelev/finagle,spockz/finagle,spockz/finagle,twitter/finagle,luciferous/finagle,luciferous/finagle