Downloading sbt launcher for 1.4.9:
From https://repo.scala-sbt.org/scalasbt/maven-releases/org/scala-sbt/sbt-launch/1.4.9/sbt-launch-1.4.9.jar
To /home/travis/.sbt/launchers/1.4.9/sbt-launch.jar
The problem most likely is, that bintray is discontinued and the new sbt release is published to github now.
If you use sbt-extras then you might need to upgrade it.
Example: