Depreciation warning from pip about matplotlib version

[goepp]

Hi,
First, thank you for your work.
Pip runs a depreciation after DESC is installed: desc 2.1.1 has a non-standard dependency specifier matplotlib>=2.2pydot.
I believe this is due to a missing comma at the end of the following line:

desc/setup.py

Line 19 in e4116d6

'matplotlib>=2.2'

Best,
Vivien