Cross-build the Scala.js project for 2.11 to simplify build
Cross-build the Scala.js project for 2.11 to simplify build

This means the 2.11 cli uses the 2.11 js client instead of 2.12.
This makes `+publish` work out of the box.

scalameta/metadoc,scalameta/metadoc,scalameta/metadoc,scalameta/metadoc