Error(s) in re-building vignettes:
--- re-building ‘demo.Rmd’ using rmarkdown
Loading required package: maps
The 7-zip program is needed to unpack NHD downloads (http://www.7-zip.org/).
dyld: lazy symbol binding failed: Symbol not found: ____chkstk_darwin
  Referenced from: /usr/local/bin/pandoc (which was built for Mac OS X 10.15)
  Expected in: /usr/lib/libSystem.B.dylib

dyld: Symbol not found: ____chkstk_darwin
  Referenced from: /usr/local/bin/pandoc (which was built for Mac OS X 10.15)
  Expected in: /usr/lib/libSystem.B.dylib

Error: processing vignette 'demo.Rmd' failed with diagnostics:
pandoc document conversion failed with error 6
--- failed re-building ‘demo.Rmd’

--- re-building ‘flow.Rmd’ using rmarkdown
Loading required package: maps
The 7-zip program is needed to unpack NHD downloads (http://www.7-zip.org/).

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Linking to GEOS 3.7.2, GDAL 2.4.2, PROJ 5.2.0
dyld: lazy symbol binding failed: Symbol not found: ____chkstk_darwin
  Referenced from: /usr/local/bin/pandoc (which was built for Mac OS X 10.15)
  Expected in: /usr/lib/libSystem.B.dylib

dyld: Symbol not found: ____chkstk_darwin
  Referenced from: /usr/local/bin/pandoc (which was built for Mac OS X 10.15)
  Expected in: /usr/lib/libSystem.B.dylib

Error: processing vignette 'flow.Rmd' failed with diagnostics:
pandoc document conversion failed with error 6
--- failed re-building ‘flow.Rmd’

--- re-building ‘network.Rmd’ using rmarkdown
Loading required package: maps
The 7-zip program is needed to unpack NHD downloads (http://www.7-zip.org/).

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Linking to GEOS 3.7.2, GDAL 2.4.2, PROJ 5.2.0
Warning in st_centroid.sf(mendota_lake) :
  st_centroid assumes attributes are constant over geometries of x
Warning in st_centroid.sfc(st_geometry(x), of_largest_polygon = of_largest_polygon) :
  st_centroid does not give correct centroids for longitude/latitude data
dyld: lazy symbol binding failed: Symbol not found: ____chkstk_darwin
  Referenced from: /usr/local/bin/pandoc (which was built for Mac OS X 10.15)
  Expected in: /usr/lib/libSystem.B.dylib

dyld: Symbol not found: ____chkstk_darwin
  Referenced from: /usr/local/bin/pandoc (which was built for Mac OS X 10.15)
  Expected in: /usr/lib/libSystem.B.dylib

Error: processing vignette 'network.Rmd' failed with diagnostics:
pandoc document conversion failed with error 6
--- failed re-building ‘network.Rmd’

SUMMARY: processing the following files failed:
  ‘demo.Rmd’ ‘flow.Rmd’ ‘network.Rmd’

Error: Vignette re-building failed.
Execution halted