Propagating changes to "sonatypePublishTo" and "publishTo" to subprojects.

[atooni]

This fixes #76

[xerial]

@atooni Thanks for the PR.

It looks good to me, except the fix is not working for sbt 0.13.x.
Now that we don’t need to support sbt 0.13.x we can drop the support for 0.13.x to pass this PR.

Did you test this fix on your project?

[atooni]

@xerial I noticed travis failing. I think this is because I used the new slash syntax for my changes. I am late to the game of sbt and have only briefly looked at it before. We have just migrated to sbt and have used 1.2.3, so I canẗ really speak for 0.13.x.

If you are happy to drop 0.13.x support for future releases, for me that is perfectly fine. On my own project the fix seems to work as expected and I am able to publish all my aggregates to sonatype with it.

For reference: Our project lives in https://github.com/woq-blended/blended; I am just trying to get auto releases via travis working for me.

[xerial]

Let me merge this first, then I will drop sbt 0.13 support