Fix `date`: All values are missing.

[maurolepore]

all(is.na(fgeo.data::luquillo_tree5_random$date))
#> [1] TRUE
all(is.na(fgeo.data::luquillo_stem5_random$date))
#> [1] TRUE
# Is the problem comming from rtbl?
all(is.na(fgeo.data::luquillo_vft_4quad$Date))
#> [1] FALSE

Created on 2018-09-28 by the reprex package (v0.2.1)