According to various blog posts of the official github developer website
[1] [2], the mime preview for Releases and Search are no longer needed.
Moreover, they recommend to use `application/vnd.github.v3+json` for
every requests.

[1] http://developer.github.com/changes/2013-11-04-releases-api-is-official/
[2] http://developer.github.com/changes/2013-10-29-search-api-becomes-an-official-part-of-github-api-v3/

Includes Repositories.ListReleaseAssets, Repositories.GetReleaseAsset,
Repositories.EditReleaseAsset, Repositories.DeleteReleaseAsset,
Repositories.UploadReleaseAsset.

include Repositories.ListReleases, Repositories.GetRelease,
Repositories.CreateRelease and Repostories.DeleteRelease.