Rake tests fail on MongoDB version 3.6.8

[camiloforero]

When running bundler exec rake I got two errors. Attached is the stdout of that command:
tests.txt (if you cat it, it will look nice with colors just as with rake)

When trying to get to the bottom of it, I found out that after MongoDB version 3.2, a new version of indexes is being used https://docs.mongodb.com/manual/core/2dsphere/ . I have MongoDB version 3.6, so that could be the cause, but apparently your travis tests are passing with a MongoDB version 3.2 so I'm not so sure

One possible fix would be to force the creation of Version 2 indexes. Or to just ignore the version number when doing the check on the tests. Or to check against which version to compare, according to the MongoDB version

[dblock]

I think the first step is to reproduce this in CI. Make a pull request that swaps the version of MongoDB? I believe you should be able to have a set of tests use 3.2 and another use 3.6 within the same .travis.yml.