Add generic type safety for useLocation state data

[boylett]

Currently, useLocation is non-generic, and the state data returned by it is simply typed as any.

The Location type already supports state typing, so it should be trivial to implement a generic for useLocation.

// react-router/lib/hooks.tsx - 133

-export function useLocation(): Location {
+export function useLocation<State = any>(): Location<State> {