That library uses callbacks and isn't really related other than the name. I don't think that the author googled async.js to see if the library name was already taken.
https://github.com/eligrey/async.js: 15 stars on Github
Sorry, you lost this one.
It's annoying (it's happened to me too) but I don't think there's much you can do about it. Especially when the name is incredibly generic.