(WIP)(FACT-728) Update Windows OS release resolution for > 6.2.x kernels

Currently, Facter only knows how to deal with Windows kernels
up to 6.2.x for parsing out the operating system release value.
Windows 8.1 and 10 use kernel versions 6.3.x and 6.4.x
respectively, which cause Facter to fall back to reporting the
kernel version as the operating system release, instead of the
strings "8" or "10" as it should.

This commit adds a check for kernel versions starting with "6.3"
or "6.4" to resolve this issue.
I don't think there is yet a Windows Server skew with 6.4, but if/when it happens (producttype != 1), this fact will return nil instead of falling through to the else clause below. We may want to be more proactive about that?

<pre>
when /^6\.4/
  os.producttype == 1 ? "10" : Facter[:kernelrelease].value
</pre>