fix: include vanity url in `get_content()` results

[toph-allen]

get_content()'s documentation states that the content URL either contains the content URL or the vanity URL for a content item:

connectapi/R/get.R

Lines 176 to 177 in 02acf5e

	#' * `content_url`: The URL associated with this content. Computed
	#' from the associated vanity URL or GUID for this content.

This is not the case; it only fetches the regular "open solo" URL. It should function as documented.