update for tibble-2.0.0

[r2evans]

cellranger::cell_addr(1:3, 2)
# <cell_addr: 3 cells>
# Warning: `as_data_frame()` was deprecated in tibble 2.0.0.
# Please use `as_tibble()` instead.
# The signature and semantics have changed, see `?as_tibble`.
# This warning is displayed once every 8 hours.
# Call `lifecycle::last_lifecycle_warnings()` to see where this warning was generated.
# # A tibble: 3 x 2
#     row   col
#   <int> <int>
# 1     1     2
# 2     2     2
# 3     3     2