Edit changelog and include 1.6.8 release notes.

Author: jxblum

spring-geode-project/spring-geode/src/main/resources/changelog.txt

@@ -4,6 +4,15 @@ https://github.com/spring-projects/spring-boot-data-geode
 =========================================================
 
 
+Changes in version 1.6.8 (2022-05-19)
+-------------------------------------
+Aligns SBDG with Spring Boot 2.6.8.
+
+* Built with Java 8, JDK 1.8.0_331.
+* Upgrades to Spring Framework 5.3.20.
+* Upgrades to Spring Boot 2.6.8.
+
+
 Changes in version 1.5.14 (2022-05-19)
 --------------------------------------
 Aligns SBDG with Spring Boot 2.5.15.