arrow

ARROW-5574: [R] documentation error for read_arrow()

@wesm this should fix the current R related issues on travis. I'll merge once travis gives the ✅

Author: Romain Francois <romain@rstudio.com>

Closes #4530 from romainfrancois/ARROW-5574/read_arrow_doc_error and squashes the following commits:

cd83b1da <Romain Francois> use_threads= argument of read_arrow() is obsolete