Bump jackson-databind to 2.10.5.1

Update website Proguard rule section to be same as Readme

Fixing dead link

Java 15 final

Gradle 6.7 RC1 for offical Java 15 support

Prevent use of Java 8 classes on RoboVM

Update google-java-format to 1.8

Fix typo in release doc

Error-prone 2.4.0

Fix typo

Use https for the apache license

Update document:retrofit use gradle as build tool,maven cmd not works.

Added RxJava3 adapter

OkHttp 3.14.9

This contains the fix for Android detection on the OkHttp side.

Move source/target config out of error-prone block

Error-prone only works on pre-12 at the moment and we need this configuration to apply for all JDKs.

Use system properties to detect Android

Android classes can show up on the classpath on the JvM in places like IntelliJ when you have the Android plugin applied.