pyflow fails to find dependancy for cairocffi

[tanj]

When installing CairoSVG in a pyflow project a dependency is missed for a supporting package cairocffi

The missing dependency is cffi

1. pyflow 0.2.9
2. pyflow new test_project
3. cd test_project
4. pyflow install cairosvg
5. pyflow list

 % pyflow list
These packages are installed:
cairocffi == 1.2.0
CairoSVG == 2.5.2
cssselect2 == 0.4.1
defusedxml == 0.7.1
Pillow == 8.1.2
tinycss2 == 1.1.0
webencodings == 0.5.1

These console scripts are installed:
cairosvg

expecting cffi to be installed as it is a dependency of cairocffi