Make startYear setting deterministic

[armanbilge]

Instead of defaulting to the current year (this was a bad default, I'm sorry) it now defaults to the current year at the time that version of sbt-typelevel was built.

[mzuehlke]

Do you think even having a default for startYear is a good idea in the first place ?
I think it is mostly (exclusively ?) used for the header generation and wouldn't this result in the header being updated each year when we drop a new sbt-tl release ?

The official meaning is

val startYear = settingKey[Option[Int]]("Year in which the project started.").withRank(BMinusSetting)

https://github.com/sbt/sbt/blob/0c6d7b8f300f1e405e2a2db5d84f72d30a7ec901/main/src/main/scala/sbt/Keys.scala#L342

[armanbilge]

Do you think even having a default for startYear is a good idea in the first place ?

That's a good point. I think I gave it a default to make the "getting started" experience as fast and easy as possible. But I guess the proper place to do this is in templates where startYear is set appropriately to a fixed year.