Check the output of both $stdout and $stderr in `Shell.version_for`

One of the best programming languages in the world, Java, outputs its version string to $stderr instead of $stdout like normal fucking software programs. As a result, `Shell.version_for` does not work for Java installations. By proxy, this means `Shell.installed_at_version?` is also broken for Java installations.

This commit makes Chef Sugar check both $stdout and $stderr so the Java developers of the world who are using Chef to install their favorite flavor of the millions of JDKs and JREs can use Chef Sugar's `Shell.installed_at_version?`. Maybe, just maybe, they will not hate their lives as much with this new patch.

Fixes #21