update links. scalaz-seven is no longer maintenanced

- https://groups.google.com/d/topic/scalaz/4gKSSYwpKxE/discussion
- https://github.com/scalaz/scalaz/commit/0a5f2e9b9c1db0e90ff873909033cb7fb313a989#diff-04c6e90faac2675aa89e2176d2eec7d8R122
 - https://github.com/scalaz/scalaz/blob/0a5f2e9b9c1db0e90ff873909033cb7fb313a989/core/src/main/scala/scalaz/OptionT.scala#L23
 - https://github.com/scalaz/scalaz/blob/0a5f2e9b9c1db0e90ff873909033cb7fb313a989/core/src/main/scala/scalaz/OptionT.scala#L59