Use Spring Data Gosling snapshots

Upgrade to Spring Data Gosling snapshot version in preparation for
Gosling-M2.

See gh-3288

spring-boot-dependencies/pom.xml

@@ -125,7 +125,7 @@
 		<spring-amqp.version>1.5.0.M1</spring-amqp.version>
 		<spring-cloud-connectors.version>1.1.1.RELEASE</spring-cloud-connectors.version>
 		<spring-batch.version>3.0.4.RELEASE</spring-batch.version>
-		<spring-data-releasetrain.version>Gosling-M1</spring-data-releasetrain.version>
+		<spring-data-releasetrain.version>Gosling-BUILD-SNAPSHOT</spring-data-releasetrain.version>
 		<spring-hateoas.version>0.17.0.RELEASE</spring-hateoas.version>
 		<spring-integration.version>4.2.0.M1</spring-integration.version>
 		<spring-loaded.version>1.2.3.RELEASE</spring-loaded.version>