[proposal] Only using node testing tools about superagent

[jimmywarting]

I have not been such a huge fan of things such as res.text.should.equal('{"name":"hal 5000"}');

should pollutes global built in prototypes chain with things you believe are part of the package when it is in fact not.

[titanism]

Definitely down to use built-in Node test stuff, either that or Ava like we did with https://github.com/breejs/bree

[jimmywarting]

I prefer dependency free stuff.
now that NodeJS have also a built in test runner also node:test and also a node:assert, then i have stop installing any additional dependencies.

the latest version of node testing tools have really grown to be something 👌