refactor: use prfun for extended Promise API

Closes #44
refactor(tasks/support/jscs): use prfun to make code simpler

We are using prfun for an extended Promise API, but we can't be sure that
third-party libraries will return a standard Promise. For example, jscs uses
another Promise library.

Therefore, we have to wrap the Promise with `Promise.resolve()` in order to
be able to use the extended API.