Add basic auth option to lazyimages_without_scroll_events.js

[Diego Durán]

Sometimes people wants to tests lazy loads on basic auth protected websites (usually on preproduction environment).

I wish propose a new yarg option to pass basic auth to website in the file lazyimages_without_scroll_events.js.

Eg: node lazyimages_without_scroll_events.js -b username::password -u https://example.com