Update for numpy int deprecation.

[wtgee]

• Replace all np.int instances with just int.

Reference: https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations

Mentioned by @thusser in the astroplan slack channel. Thanks!

[bmorris3]

Thanks for getting on this so quick @wtgee! I've just added a commit that fixes the style checks.