Update to new template from g8

Seems that support for project/plugins/* plugin configuration will be removed in next sbt release. Default g8 template created by using

    g8 n8han/giter8

does not have this issue, so I updated it to reflect upstream change.

For reference of why such changes, see:

 - http://www.scala-sbt.org/snapshot/docs/Community/ChangeSummary_0.13.0.html
 - http://www.scala-sbt.org/0.12.1/docs/Detailed-Topics/Migrating-from-sbt-0.7.x-to-0.10.x.html#create-build-sbt-for-version
 - https://github.com/n8han/giter8#using-the-giter8-plugin