Polish formatting in DefaultEntityResponseBuilder

[hydrationn]

This PR applies a minor formatting polish in DefaultEntityResponseBuilder
by adding a missing space after a comma for improved readability.

- writeEntityWithMessageConverters(this.entity, servletRequest,servletResponse, context);
+ writeEntityWithMessageConverters(this.entity, servletRequest, servletResponse, context);

[bclozel]

Thanks for the suggestion, but we'd rather not spend time processing PRs for single char, cosmectic changes. We have checkstyle rules that are already quite complete. We'll eventually fix this but it's not worth spending much time on this.