Metals: Don't import builds older than sbt 0.13.17

[rrodseth]

Submitting as requested on Gitter.
I got the error below while importing an sbt file in VS Code after installing Metals:
Turns out the project I opened did have sbt.version=0.13.8 in build.properties After changing that to 1.1.6 I can import.

>
/Users/rrodseth/.sbt/0.13/plugins/metals.sbt:12: error: not found: value pluginCrossBuild
val sbtVersion = Keys.sbtBinaryVersion.in(pluginCrossBuild).value
<<<

[olafurpg]

Thanks for reporting! It's expected that Metals doesn't work with sbt 0.13.8, but it works with 0.13.17 so it's not necessary to upgrade to sbt v1 to work around the issue.

[olafurpg]

Reopened ticket to be about improving the error message for builds older than 0.13.17.