Maintenance/deprecation futurewarn updates

[sablanchard]

• addresses: Misc DeprecationWarning and FutureWarnings #26
• update requirements to: geopandas >= 0.8.2 and shapely >= 1.6
• drops Python 3.7 from tests for now due to Travis build error
• updates contribution guidelines

[coveralls]

Coverage increased (+3.1%) to 92.604% when pulling eaad726 on maintenance/depreciation-futurewarn-updates into dce59a3 on dev.

[smmaurer]

Nice! Looks good to me.

Bumping the GeoPandas requirement to v0.9+ means ending support for Python 3.5, which we should note in setup.py (drop line 20, change line 28 to 3.6).

The Travis tests are failing in Python 3.5 (of course), but also 3.7 because of a Travis glitch. My recollection of what's happening is that their py37 image includes a copy of NumPy already installed, but it's a little old and ends up being incompatible with the copy of Pandas that's installed from PyPI. We've seen this in other repos too.

https://travis-ci.org/github/UDST/osmnet/builds/765409781

It's been a couple of months without a fix on their end, so my inclination is to drop Python 3.7 from our test script (along with 3.5).

https://github.com/UDST/osmnet/blob/dev/.travis.yml#L6

[sablanchard]

Agreed, dropped tests in 3.7 for now. Decided to set geopandas >= 0.8.2 to preserve compatibility with Python 3.5