"Unknown option --export-png" when installing

Created by: vinliao

i have all the needed dependencies installed and I get this error

Rendering /home/vinliao/Code/Mojave-gtk-theme/src/assets/cinnamon/thumbnail-light.png
Unknown option --export-png=/home/vinliao/Code/Mojave-gtk-theme/src/assets/cinnamon/thumbnail-light.png

Rendering /home/vinliao/Code/Mojave-gtk-theme/src/assets/gtk-3.0/thumbnail-light.png
Unknown option --export-png=/home/vinliao/Code/Mojave-gtk-theme/src/assets/gtk-3.0/thumbnail-light.png

Rendering /home/vinliao/Code/Mojave-gtk-theme/src/assets/metacity-1/thumbnail-light.png
Unknown option --export-png=/home/vinliao/Code/Mojave-gtk-theme/src/assets/metacity-1/thumbnail-light.png

Rendering /home/vinliao/Code/Mojave-gtk-theme/src/assets/cinnamon/thumbnail-dark.png
Unknown option --export-png=/home/vinliao/Code/Mojave-gtk-theme/src/assets/cinnamon/thumbnail-dark.png

Rendering /home/vinliao/Code/Mojave-gtk-theme/src/assets/gtk-3.0/thumbnail-dark.png
Unknown option --export-png=/home/vinliao/Code/Mojave-gtk-theme/src/assets/gtk-3.0/thumbnail-dark.png

This might be because of missing some dependencies, but that's just my guess.