exclude specs2 from lift-json
https://github.com/lift/framework/issues/1397
http://d.hatena.ne.jp/xuwei/20130130/1359498947
https://github.com/lift/framework/blob/2.5-M4-release/project/Dependencies.scala#L86
Merge pull request #2 from xuwei-k/exclude-specs2

exclude specs2 from lift-json