`sbt` script under `develop` branch is out of date

[rnowling]

When I tried to use the sbt script to build silex, the script reported an error about retrieving sbt-launch.jar. I noticed that it tried to use the old artifactoryonline.com repo. Updated the sbt script fixed the issue for me.

[willb]

@rnowling I'm going to propose instead that we drop the bundled sbt. Bundling sbt is an antipattern that a lot of projects do simply because a lot of other projects do. Furthermore (given when the Typesafe/Lightbend artifacts moved), it seems like you're the only person to have used it since last summer!

[rnowling]

I actually like having the sbt runner in my projects; having all dependencies contained within a project makes it very, very easy. I disagree with unbundling. We could use the sbt runner in Travis, and thus, it would be tested more regularly to prevent future issues. :)