Get A Tag

Returns the specified tag.```$ curl -s https://api.bitbucket.org/2.0/repositories/seanfarley/hg/refs/tags/3.8 -G | jq .{ "name": "3.8", "links": { "commits": { "href": "https://api.bitbucket.org/2.0/repositories/seanfarley/hg/commits/3.8" }, "self": { "href": "https://api.bitbucket.org/2.0/repositories/seanfarley/hg/refs/tags/3.8" }, "html": { "href": "https://bitbucket.org/seanfarley/hg/commits/tag/3.8"