Use Travis CI default sbt and extend build matrix
Merge pull request #247 from gildegoma/scalaz-seven-travisci-fullmatrix

Travis CI: Extend the build matrix for Scalaz Seven branch
Revert "updated SBT plugins"

sbt-release plugin depends on the task "publish", but sbt-pgp doesn't sign
artifacts in "publish" anymore.

This reverts commit 75213e92533c8abb2bcc1b7a542aa0fc07026a6e.
Releasing 7.0.0-M8
Bump to 7.0-SNAPSHOT