Resolve "Upgrade spring-boot dependency (2.2.11 instead off 2.2.3)"

Closes #551 (closed)

see:

• https://spring.io/blog/2020/10/29/spring-boot-2-2-11-available-now
• https://spring.io/blog/2020/09/17/spring-boot-2-2-10-available-now
• https://spring.io/blog/2020/07/24/spring-boot-2-2-9-available-now
• https://spring.io/blog/2020/06/11/spring-boot-2-2-8-available-now
• https://spring.io/blog/2020/05/07/spring-boot-2-2-7-available-now
• https://spring.io/blog/2020/03/26/spring-boot-2-2-6-available-now
• https://spring.io/blog/2020/02/27/spring-boot-2-2-5-released
• https://spring.io/blog/2020/01/20/spring-boot-2-2-4-released