Update to Spring Framework 5.2.8.RELEASE

Closes gh-8919

gradle/dependency-management.gradle

@@ -3,7 +3,7 @@ if (!project.hasProperty('reactorVersion')) {
 }
 
 if (!project.hasProperty('springVersion')) {
-	ext.springVersion = '5.2.6.RELEASE'
+	ext.springVersion = '5.2.8.RELEASE'
 }
 
 if (!project.hasProperty('springDataVersion')) {