Add rule prefer `() -> ` over `Void -> `

[norio-nomura]

Related to #570, we talked about another this.
In apple/swift, we can't find Void ->.
#570 can also be avoided by this.

[masters3d]

@eyeballz
related #717

[kutschenator]

how did i not see this :/
http://ericasadun.com/2015/05/11/swift-vs-void/ should be enough as "source of truth" to make a rule out of it. Don't have too much time at the moment but I will try to code this very soon.

[jpsim]

@eyeballz I see you were once interested in writing this rule. Are you still interested in contributing to SwiftLint? Do you have any questions on how to proceed? I'm happy to help 😄

[kutschenator]

Yes! I am actually waiting for the swift 3 migration #832 to finish. Then I will be right on it