Add numpy to the list of dependencies

[firefly-cpp]

proplot package is an exciting as well as powerful package. Thanks for all the hard work (@lukelbd). I am maintaining this package in the Alpine Linux ecosystem.

I recommend you add numpy to the list of dependencies for correctness. Some files import this package.

[syrte]

(I am no familiar with the convention about dependency list, just to a random comment.)
proplot depends on matplotlib, which in turn depends on numpy.
so in principle, the dependence on numpy should be resolved automatically?

[firefly-cpp]

For the sake of correctness, it is good to include all dependencies you import, although they are being installed automatically. It is also good to ensure in case any dependency chain changes during the software evolution.

Finally, from the package maintenance perspective is good to have all main dependencies in the dependency list to mitigate breakages quickly.

[lukelbd]

Thanks for the PR and the kind words.

@syrte that was indeed my logic -- matplotlib imports numpy, so matplotlib is "effectively" the only dependency. But @firefly-cpp this makes sense to me as a safe/standard rule for dependency management, since matplotlib and numpy are the two external packages I explicitly import. I'll follow the rules and merge