Fix ratpack.spring.Spring javadoc's java example, upgrade to Spring Boot 1.1.6.RELEASE

this PR contains 2 small improvements: a fix to the ratpack.spring.Spring javadoc's java example and upgrades the Spring Boot dependency to 1.1.6.RELEASE version.

@danveloper asked me if the java example intentionally creates a new Spring context instance for each request. This PR should fix that problem in the code example.