make dynamic mock callable

[mpodlasin]

Hi.

I use your library in my side project and really like it so far. Great solution for mocking typed code, especially with es6 proxy mocks!
That being said I encountered small issues, so here is my proposition of fix:

Calling proxied function (dynamic mock implemented with es6 proxy to be precise) is impossible right now.
Code

const fnMock = Mock.ofType<Function>();
fnMock
   .setup(fn => fn())
   /* ... */

will thow error fn is not a function.

It turns out es6 proxy will be callable only if proxied object is callable.
It means that in your library line:

new Proxy({}, handler);

should be changed to

new Proxy(() => {}, handler);

Note that this is more general, since every function is an object - all dynamic object mocks will still work, and error about fn not being function will disappear.

Thanks in advance and have a great day!

[florinn]

Great insight, I've added a few related tests. Thanks for contributing.