Tests not included in pypy srcdist

[dvzrv]

The pypi source tarball does not provide the tests. Please include them!
I'm packaging tmuxp for Arch Linux and we usually try to exclusively use the pypi sources for python packages.

[tony]

@dvzrv Adding. Anything else that'd be helpful? (#432 needs to be clarified also, do you use Pipfile? Can you show me an example of a requirements file with pins that wouldn't block downstream?)

[tony]

v1.4.2 is live on pypi for tests

also v1.4.1 loosens click restraint to <7