3.1.2 release preparations

[akarnokd]

Version 3.1.2 - October 8th, 2021

Maven
JavaDocs

Compatibility

• Add full Java 9 module descriptor. (#7241)

Bugfixes

• Fix missing nullability on Single.subscribe(BiConsumer). (#7331)

Documentation

• Fix javadoc wording of {Publish|Behavior}Processor::offer(). (#7328)
• Indicate takeUntil stops on completion of other. (#7341)

Other

• Update assert messages format to be compliant with GradleRunner and JUnitRunner. (#7345)

[akarnokd]

Closing via v3.1.2