Distinct requirements for PR, branch, and cron builds

[marcospereira]

Distinct requirements for PR, branch, and cron builds

Let's define requirements that are more appropriate for each one of the types of builds.

Versions

Primary and secondary versions are:

master branch

What	Primary	Secondary
Scala	2.13.0	2.12.8
Java	8	11
sbt	1	0.13

stable supported branches

What	Primary	Secondary
Scala	2.12.8	2.11.12 and 2.13.0 where applicable
Java	8	11 where applicable
sbt	1	0.13

Jobs for each type of build

pull requests

1. docs: check format and headers
2. docs: run tests
3. framework: check format, headers and binary compatibility*
4. framework: run tests using main Scala version and Java version
5. framework: run scripted tests using main sbt version and Java version

_{\* These are lightweight enough to run cross scala versions}

branches

All pull requests jobs plus:

1. framework: run tests using secondary Scala version and main Java version
2. framework: run scripted tests using secondary sbt version and main Java version

crons

All branches jobs plus:

1. framework: run tests using the main Scala version and secondary Java version
2. framework: run scripted tests using main sbt version and secondary Java version

Originally posted by @marcospereira in #98 (comment)

[mkurz]

I don't think this matters anymore... It's from old ancient times we used Travis, we figured out our system with GitHub actions now.