add onLocationChanged method typings

[goszczynskip]

This PR will add missing typescript typings for exposed onLocationChange method. Issue: #246

[salguerooo]

@goszczynskip Even though this actions is being exported on the actions files, it is not made public for users of the library, it is for internal use, as can be seen on this line of the index.js
export { LOCATION_CHANGE, CALL_HISTORY_METHOD, push, replace, go, goBack, goForward, routerActions } from "./actions"
it shouldn't be typed as it is not possible to use it.

[goszczynskip]

@salguerooo If you look at snippet below you'll see that it's exported in index.js file.

connected-react-router/src/index.js

Line 6 in 3977f3b

export { LOCATION_CHANGE, CALL_HISTORY_METHOD, onLocationChanged, push, replace, go, goBack, goForward, routerActions } from "./actions"

I'm listening for LOCATION_CHANGE action in redux-observable epic. It'd be nice if I could use onLocationChange action creator in my typescript tests. Since typings are't reflecting exported members my tests would fail. Of course I can type it in my d.ts files but I think it should be done here.

[salguerooo]

@goszczynskip My bad then! I was referencing some local outdated code.

[supasate]

LGTM. Thanks for your contribution!

[nikolay-borzov]

I believe you cannot use parameter initializer (isFirstRendering: boolean = false) inside a definition file.
TS complains:

A parameter initializer is only allowed in a function or constructor implementation

[goszczynskip]

@nikolay-borzov Yes, you are right. I can see that fix is waiting for merge so I won't create new one.

I'm sorry for any trouble caused by this.