Example use of whenever should use a react block

[jmaslak]

The problem

whenever needs to be in a react block (looks like a 6.d feature).

Solution provided

Wrapped the usage of whenever in a react block within the example for listen().

Also added myself to CREDITS.

[zoffixznet]

I sent you an invite to perl6 GitHub org that gives you access to most of our repos. You can accept it here: https://github.com/perl6/

Once you do, you will be able to merge this PR yourself and commit future work directly.

[jmaslak]

Thanks!

I'll merge this tomorrow assuming nobody comments that they have issues with it.

[JJ]

Since you are not using $big-finish any more, could that declaration be eliminated?