Update Java Buildpack

This change updates the Java Buildpack submodule to version 1.3. Version 1.3 includes the following improvements:

* Unpinned the OpenJDK JRE range to allow automated updates beyond 1.7.0_21
* Improvements to the behavior of the buildpack when no network connection is available
* Introduction of component base classes to ease extension of the buildpack
* Support for executing Groovy applications with files in directory trees
* Support for bounding memory regions
* CentOS6 support