Fix segments parsing for optional segments

/api/:version/groups/:id/(-/)search(.:format) is currently parsed into the segments

["api", ":version", "groups", ":id", "(-", ")search"]

This merge request changes that to

["api", ":version", "groups", ":id", "(-/)", "search"]

see also http://rubular.com/r/L7Dd2RRrpn