Tighten History.go() param type

[danielnixon]

History.go() currently accepts a delta: js.Any. We can tighten this up to delta: Int|String if we want to continue to support IE's non-standard behavior, or even tighter to delta: Int if we don't.

[sjrd]

I'd say Int. scalajs-dom is supposed to represent the standard, unless there is a compelling reason not to.

[andersschuller]

As far as I can tell based on the MDN docs and this spec, this isn't the only issue with the navigation methods in History. The back and forward methods can currently take a single distance parameter, but the links above list them as being parameterless.

In a minute I'll create a pull request to fix both of these issues.