Upgrade zinc to 1.4.0

[jroylance]

No description provided.

[SrodriguezO]

Builds are failing: https://travis-ci.org/github/higherkindness/rules_scala/builds/739988853

The status doesn't on the PR update cause of #288... I'll reach out to James to see if we can get that taken care of

[timothyklim]

Version 1.4.0 has breaking changes:

• VirtualFile and VirtualFileRef instead of Path;
• compiler-bridge.jar must contain META-INF/services/xsbti.compile.CompilerInterface2 or it will throw NPE because of switching to legacy xsbti.CompilerInterface which not available in classpath;
• No ScalaPB for sbt internal messages! Only messages from shaded google protobuf package.

I have a fork (https://github.com/TimothyKlim/rules_scala/pull/1/files) which I'm using to upgrade zinc to 1.4.2, drop old scala versions and add scala 3.0.

[jroylance]

Awesome. @timothyklim do you have plans to merge your fork back here once it's working?

[timothyklim]

Now I can build and test my project with this commit.
You can cherry-pick changes that you need to continue backwards compatibility, I have my fork to have ability to move fast and break things until I'll port rest things to get rid of sbt.