fix: preserve basic auth in nodejs if present

[garbados]

This PR closes #64 by using the username and password values parsed from the request URL to populate the auth option used by nodejs http/s.

[garbados]

I didn't include a test because this modifies the nodejs.js file, which is not tested by the test suite. I did try, but the core mkrequest method rejects basic auth that hasn't been converted to a header:

TypeError: Failed to execute 'fetch' on 'Window': Request cannot be constructed from a URL that includes credentials: http://admin:password@localhost:5984

[mikeal]

I didn't include a test because this modifies the nodejs.js file, which is not tested by the test suite.

It’s definitely tested, including coverage testing.

[mikeal]

Ok, I pulled this down, added a test and got it working for browsers as well.

[garbados]

It’s definitely tested, including coverage testing.

Sorry, you're right. I misread the instrumentation.