3.0.7 release preparations

[akarnokd]

Version 3.0.7 - October 7, 2020 (Maven)

JavaDocs

Bugfixes

• Fix Observable.toFlowable(ERROR) not cancelling on MissingBackpressureException. (3.x: Fix toFlowable(ERROR) not cancelling on MBE #7083)
• Fix Flowable.concatMap backpressure with scalars. (3.x: Fix Flowable.concatMap backpressure w/ scalars #7089)

Documentation

• fromRunnable/fromAction javadoc improvements. (3.x: fromRunnable/fromAction javadoc improvements #7071)
• Patch out duplicate @NonNull annotation in generated javadocs. (3.x: Patch out duplicate @NonNull annotation in generated javadocs #7073)
• Clarify the documentation for scan operators. (Clarify the documentation for scan operators #7093)

[akarnokd]

Closing via https://github.com/ReactiveX/RxJava/releases/tag/v3.0.7