Update start year in template

[armanbilge]

https://github.com/typelevel/typelevel.g8/blob/67ee77a0e68f587ff57a0d19fd610445ee9c20c8/src/main/g8/build.sbt#L6

If we could make this a configurable property that seems even better, then I think we would only need to bump it in one place and the user can easily set it to a different year.