upgrade select() to new tidyselect

[romainfrancois]

So we can do e.g.

library(dplyr, warn.conflicts = FALSE)

iris %>% 
  select(is.numeric)
#> Error: This tidyselect interface doesn't support predicates yet.
#> ℹ Contact the package author and suggest using `select_pos()`.

^{Created on 2019-12-30 by the reprex package (v0.3.0.9000)}