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
Merge pull request #72 from nebhale/update-java-buildpack

Update Java Buildpack