Fix for wrong offset values when onDoubleTapAfter is fired

[ajayg415]

This is fix for Problem statement #60

I have moved the onDoubleTapAfter into this.setState call back. this will ensure user will get correct offsetX and offsetY.

Please review, we're using this component in one of our project and this fix will help us to deliver bug free code.

Appreciate your efforts. :)

[SimonErich]

@ajayg415 Thank you very much for your contribution.
I have checked it out, but I would like to keep the Codestructure as it is with zoomToLocation still abstracted.

Fortunately zoomToLocation was already prepared to receive a callback parameter, that will be triggered after state was changed, so I implemented it in #63 and merged it in.

With the next release onward the problem should be solved.

Thank you very much for your pull request though. I am closing it here, but only because I took your solution and implemented it differently.

[ajayg415]

Thanks for your quick response @SimonErich. I thought this will become my first open source contribution, but its ok. Thanks again :)

[SimonErich]

Sorry @ajayg415 but keep them coming!
I really appreciated your PR. In fact your work on issues and the pr motivated me to make the take the time and make the current imrpovements on the package. :)

I would really appreciate your working help in the future as well :)