Java Buildpack v2.6

This change updates the Java Buildpack to version `2.6`.  Version `2.6` has the following highlights:

* Print `OutOfMemory` diagnostics to Loggregator (via Troy Astle)
* Support for custom CA certificates when download from a repository (via Dave Head-Rapson)
* Tomcat Redis Session Replication support for alternate Redis services (via Neil Aitken)
* Improved SSL Diagnostics

Both the online and offline buildpacks are updated as part of this change.