Switch from the abandoned `docopt` to the maintained `docopt-ng` #409

Job	Run time
build (3.7)	28s
build (3.8)	22s
build (3.9)	23s
build (3.10)	36s
build (3.11)	25s
build (3.12)	36s
Indicate completion to coveralls.io	0s
	2m 50s

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