Upgrade to Gradle 4.2.1

Issue: SPR-15985

Author: jhoeller

build.gradle

@@ -125,8 +125,8 @@ configure(allprojects) { project ->
 
 	repositories {
 		maven { url "https://repo.spring.io/libs-release" }
-		maven { url "https://repo.spring.io/milestone" }
-		maven { url "https://repo.spring.io/snapshot" }
+		maven { url "https://repo.spring.io/milestone" }  // for AspectJ 1.9 beta
+		maven { url "https://repo.spring.io/snapshot" }  // for Reactor Bismuth
 	}
 
 	dependencies {
@@ -269,7 +269,7 @@ configure(rootProject) {
 
 	task wrapper(type: Wrapper) {
 		description = "Generates gradlew[.bat] scripts"
-		gradleVersion = '4.2'
+		gradleVersion = '4.2.1'
 
 		doLast() {
 			def gradleOpts = "-XX:MaxMetaspaceSize=1024m -Xmx1024m"

gradle/wrapper/gradle-wrapper.jar

@@ -2,4 +2,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.2-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.2.1-bin.zip