Bump up sbt-extra to the latest
Bump up sbt-extra to the latest

The version of sbt-extra currently used by Travis CI downloads
sbt launcher JAR from the wrong URL, which was
fixed in paulp/sbt-extras#107.
This surfaced recently when Typesafe moved the underlying implementation
of repo.typesafe.com from artifactoryonline.com to Bintray,
and a release of new sbt version 0.13.9-M1.

Acidburn0zzz/travis-cookbooks,Acidburn0zzz/travis-cookbooks,spurti-chopra/travis-cookbooks,ljharb/travis-cookbooks,dracos/travis-cookbooks,spurti-chopra/travis-cookbooks,Distelli/travis-cookbooks,gavioto/travis-cookbooks,Acidburn0zzz/travis-cookbooks,ljharb/travis-cookbooks,dracos/travis-cookbooks,gavioto/travis-cookbooks,Zarthus/travis-cookbooks,dracos/travis-cookbooks,Acidburn0zzz/travis-cookbooks,Distelli/travis-cookbooks,gavioto/travis-cookbooks,Zarthus/travis-cookbooks,travis-ci/travis-cookbooks,Distelli/travis-cookbooks,gavioto/travis-cookbooks,Zarthus/travis-cookbooks,travis-ci/travis-cookbooks,spurti-chopra/travis-cookbooks,Distelli/travis-cookbooks,travis-ci/travis-cookbooks,dracos/travis-cookbooks,Zarthus/travis-cookbooks,ljharb/travis-cookbooks