Move spring-webmvc from spring-restdocs-core to spring-restdocs-mockmvc

[otrosien]

spring-restdocs-core does not need to depend on spring-webmvc. spring-web seems to be sufficient, at least from a compile-time pov.

[wilkinsona]

Well spotted, thank you. It's only spring-restdocs-mockmvc that needs a dependency on spring-webmvc and it's only needed at runtime.