How to change a version of dependency managed by Spring Boot in Gradle

To change the following in `spring-boot-dependencies`:

<spring-data-releasetrain.version>Gosling-RC1</spring-data-releasetrain.version>

add the following in `build.gradle`:

ext['spring-data-releasetrain.version'] = 'Gosling-M1'

Reference:
http://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#howto-customize-dependency-versions