Compile examples in the Travis build.

The subproject containing the examples (added in 8db44f35a0)
is not aggregated under the root project, and as such is not
part of `sbt compile`.

This commit adds the task `examples/compile` to the SBT command
line in the Travis CI build.

PS. I see you made your changes directly on the `jacobsallan/java7` branch. The usual GitHub workflow is to create a new branch for each pull request, and leave the real branches to track those in the upstream repository.