Drop support for scala.js 0.6.x

[Philippus]

and update scala.js 1.0.1 to 1.1.0

[exoego]

I am agraid that upgrading Scala.js to 1.1.x causes org.scalajs.ir.IRVersionNotSupportedException in projects where Scala.js 1.0.x are used.
(Maybe I am wrong ?)
Ref. scalatest/scalatest#1830

[SethTisue]

@exoego yes, if we move to 1.1 here, then downstream users must move to 1.1 as well

I also discussed this with Seb at https://users.scala-lang.org/t/announcing-scala-js-1-1-0/6053 . I was cautious enough to want to ask, as were you on the ticket you linked to, but my conclusion is: if Seb isn't worried, I'm not worried either.

we see this as well in the sbt ecosystem, where theoretically everybody ought to be building their sbt plugins on sbt 1.0.0 still, but in practice they don't and that's been okay. sometimes you have to upgrade your sbt when you upgrade a plugin

[exoego]

OK, I understood scalatest/scalatest#1830 (comment) by sjrd, and am not worrying about 1.x compatibility issue any more.