Fixed asynchronous fail, completed async success

[marcellourbani]

Saw the help request in Readme :)

I also changed asynchronous_throwable_side_effect.ts not to call any URL: an unit test is supposed to:

1. not have any external dependency (i.e. a database, a webserver,...)
2. not have side effects
3. run as fast as possible

calling an URL violates 1 and 3, possibly 2 too

Cheers Marcello