Documentation for personal snippets lists wrong parameter (code instead of content)

There is confusion over whether code or content is the right parameter for snippets. Internally, the database stores content. However:

1. Project snippets use code: https://docs.gitlab.com/ee/api/project_snippets.html#create-new-snippet. This gets remapped here to content: https://gitlab.com/gitlab-org/gitlab-ce/blob/de385eee8507a35f1c01ca784ba9aab9bc38e11d/lib/api/project_snippets.rb#L63
2. Personal snippets use content: https://docs.gitlab.com/ee/api/snippets.html#create-new-snippet

@NikolayS @eread I think the documentation in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28571 is incorrect. I think you meant to use the first version, but updated the documentation in the second.

I think we should:

1. Revert back to using content -> code in the second case
2. Consider standardizing everything around content.