Update `git lfs fetch` command

What does this MR do?

git lfs fetch master is not a valid command anymore. This changes this to include remote and branch (see https://gitlab.com/gitlab-org/gitlab-ce/commit/899807f604f7923cc40a64cdd0f61c4248b8870d#note_106074474).

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides