LFPykit-0.2rc2

LFPykit-0.2 release candidate 2

This bugfix/feature release incorporates the following changes since the 0.1 release (https://github.com/LFPy/LFPykit/releases/tag/v0.1):
da7ab3c (HEAD -> master, tag: v0.2rc2, origin/master, origin/HEAD) fix python-publish action
14bf010 (tag: v0.2rc1) version 0.2rc1
befedb8 package test scripts (#98)
a8e45a4 removed test which duplicates test in LFPy@2.2.dev0 (#96)
cb12425 added VolumetricCurrentSourceDensity class (#94)
a2ab9a1 add python3.9 to travisCI, provide wheels (#91)
b8f08d3 use official NEURON from PyPI (#89)
e9a22b5 version bump (#87)
63eb35a Fix assert statements (#86)