Add repos for Gradle plugin

* Upgrade to `com.jfrog.artifactory:4.31.1`

build.gradle

@@ -1,3 +1,10 @@
+buildscript {
+	repositories {
+		gradlePluginPortal()
+		maven { url 'https://repo.spring.io/plugins-release' }
+	}
+}
+
 plugins {
 	id 'java-library'
 	id 'eclipse'
@@ -7,7 +14,7 @@ plugins {
 	id 'checkstyle'
 	id 'org.ajoberstar.grgit' version '4.1.1'
 	id "io.spring.dependency-management" version '1.1.0'
-	id 'com.jfrog.artifactory' version '4.31.0'
+	id 'com.jfrog.artifactory' version '4.31.1'
 }
 
 description = 'Spring Integration AWS Support'