TypeNameRuleExamples: added test to verify that enum cases are lowercase in Swift 3

[NachoSoto]

To my surprise, the type_name rule is not currently validating this. I've found some issues referring to this (#655, #654, #663, and the change in #660), but it's not clear to me whether not validating this was on purpose.

So I figured I'd ask this question by sending the failing test. I'd love to have this rule validate this, but I wonder if there's a reason why this was not enabled.

Thanks.

[marcelofabri]

This will actually be fixed by #954. You can see the a similar test here: https://github.com/realm/SwiftLint/pull/954/files#diff-eb77d039fb569db405aad5349c41349aR47

That took a while because we wanted to make sure to have a deprecation warning and not just break old configurations, which is now possible thanks to #974.

[jpsim]

Closing in favor of #954.

[NachoSoto]

Awesome, thank you!