Various updates for 1.3.0

[ashawley]

This is the condensed version of about some 6 months of updates to the sbt build and Travis.

[SethTisue]

maybe .travis.yml should do the

import: scala/scala-dev:travis/default.yml 

thing like on master? not sure if you considered doing that? basically just to further reduce the differences between the branches

but, I don't have a strong feeling about it

[ashawley]

I'm only doing the minimum I can to get a Scala.js 1.0 artifact. I'm leaving off the Travis import, AdoptOpenJDK, the move to sbt-travisci and who knows what else.

[ashawley]

One concern is that publishing won't work on this old branch. If it doesn't work, I'll definitely have to consider including those subsequent build changes.