Updated dot magic, with tests

[dsblank]

This PR:

• updates the dot magic to work with current pydot
• adds tests for dot magics (cell and line)
• updates version

[dsblank]

@blink1073 How are you? I found some time to work on a couple of metakernel issues. I'm over my head on this one as I don't know github workflow syntax for how to install graphviz for the different OS test matrix entries.

[blink1073]

Hey @dsblank, I'm good, how are you? I'll push some changes :)

[blink1073]

I think it would make sense to skip the pydot tests if graphviz is not installed, to make it easier to run the tests in other environments/OSes.

[dsblank]

@blink1073 Good idea! I skipped the tests when not on linux. Thank you for your help, as always!

[blink1073]

Let me know when you're ready for a release

[dsblank]

All ready for release! Thank you!

[blink1073]

Done!