Updated travis.yml file for better test coverage

[camiloforero]

Seeing how Travisl will run with this configuration

[camiloforero]

Ok, this failed because of when all of Github failed, trying to get the tests to run again

[mongoid-bot]

	1 Warning
⚠️	Unless you’re refactoring existing code, please update CHANGELOG.md.

Here's an example of a CHANGELOG.md entry:

* [#69](https://github.com/mongoid/mongoid-geospatial/pull/69): Updated travis.yml file for better test coverage - [@camiloforero](https://github.com/camiloforero).

Generated by 🚫 danger

[coveralls]

Coverage remained the same at 95.724% when pulling 52446aa on camiloforero:master into 9d25a5a on mongoid:master.

[coveralls]

Coverage remained the same at 95.724% when pulling 52446aa on camiloforero:master into 9d25a5a on mongoid:master.

[coveralls]

Coverage remained the same at 95.724% when pulling 52446aa on camiloforero:master into 9d25a5a on mongoid:master.

[coveralls]

Coverage remained the same at 95.724% when pulling 52446aa on camiloforero:master into 9d25a5a on mongoid:master.

[dblock]

I've seen similar failures elsewhere. I think newer mongodb/mongoid created a newer index version. I didn't get a chance to track that down, would be nice to pinpoint what exactly happen and I think the fix is just to change the specs.

[dblock]

Do we want to resurrect this? You have my attention @camiloforero.

[dblock]

Let's merge #74 and add a full test matrix like in https://github.com/mongoid/mongoid_search/blob/master/.github/workflows/test.yml after