edits made to fix the vctrs type error when running tar_load on flines targets

[msleckman]

Addresses issue #46

After merge of #39 I and updates to sf, ran into issue where p1_lake_flowlines_huc8_sf could not load (only built) and therefore downstream targets p2_lake_tributaries could not build as well.

Error:

> tar_load(p1_lake_flowlines_huc8_sf)
Error:
! Can't use a name specification with non-vctrs types.
vctrs methods must be implemented for class `sfc_LINESTRING`.
See <https://vctrs.r-lib.org/articles/s3-vector.html>.
Run `rlang::last_error()` to see where the error occurred.

Seems to work when I don't use the default intereration = 'vectors' and instead use interation = 'list'`

new upstream target p1_lake_flowlines_huc8_sf_list created before binding with bind_rows into `p1_lake_flowlines_huc8_sf'

@padilla410 @jesse-ross @elmeraa curious if either you get this to work on your ends since this was something you ran into before me.