Use new version of goth to fix OpenID Connect JWT parsing issues

[willdmoore]

The latest release of Gitea uses a dependency for an older version of goth (1.45.5). This older version has a bug which causes it to improperly parse a JSON Web token (See here: markbates/goth#231). Need to update Gopkg.toml to support newer version of goth (at least 1.46.1) which will include a fix for the bug.