Upgrade samples to Spring Boot 2.2.0.RC1

Resolves: #1521

Author: vpavic

build.gradle

@@ -4,7 +4,7 @@ buildscript {
 		snapshotBuild = version.endsWith('SNAPSHOT')
 		milestoneBuild = !(releaseBuild || snapshotBuild)
 
-		springBootVersion = '2.2.0.M6'
+		springBootVersion = '2.2.0.RC1'
 	}
 
 	repositories {

spring-session-samples/gradle/dependency-management.gradle

@@ -1,10 +1,3 @@
-ext['jackson.version'] = '2.10.0'
-ext['reactor-bom.version'] = 'Dysprosium-RELEASE'
-ext['spring-data-releasetrain.version'] = 'Moore-RELEASE'
-ext['spring-framework.version'] = '5.2.0.RELEASE'
-ext['spring-security.version'] = '5.2.0.RELEASE'
-ext['webjars-locator-core.version'] = '0.38'
-
 dependencyManagement {
 	imports {
 		mavenBom 'com.fasterxml.jackson:jackson-bom:2.10.0'