Tag 2.0.0 release

[jhansche]

2.0.0 was published in Dec 2016: https://mvnrepository.com/artifact/com.facebook.device.yearclass/yearclass

but that release was not tagged:
https://github.com/facebook/device-year-class/releases

Looks like the 2.0.0 version bump landed in Master last October (27f3fee), but I don't know which commit was actually deployed to maven

[Will5]

Also the jar is not available

[zlern2k]

Eep. Time to tag 2.1.0 at this point too.