Update scalaVersion
Change crossScalaVersions a little since Specs2 for Scala 2.11.0-RC4 is not published yet
Revert "Change crossScalaVersions a little since Specs2 for Scala 2.11.0-RC4 is not published yet"

This reverts commit 6b934a85ba73e7a388cb330bd3d55fe942af4641.
Merge pull request #55 from kmizu/feature/update-scalaVersion

Update crossScalaVersions