Spring Boot 2.2.2 release, support for Gradle 6

Spring Boot 2.2.2 released, from repo.spring.io access and Maven Central.

This new version has two characteristics:

• Support constructor class binding on third parties
• Support Gradle 6. Gradle 6 is a major release, in released last month , the main highlight of this version is greatly improved feature set dependency management.

Also fixes 88 bug, and has been improved and upgraded dependency, details see:

• https://spring.io/blog/2019/12/06/spring-boot-2-2-2-is-now-available
• https://github.com/spring-projects/spring-boot/releases/tag/v2.2.2.RELEASE