Forward-port the Maven definition to use JDK 1.7.

As of 59aaced678, the Process class migrated to using Java Native I/O
StandardCharsets.  This unfortunately broke compatibility with JRE 6.0,
since this class is only available in JRE 7.0 and onward.  Thusly update
Maven model to reflect this.
Merge pull request #26 from arbeitspferde/fix/build/maven-definition

Forward-port the Maven definition to use JDK 1.7.