Safely handle a missing root user

In 657cd71 it was assumed that Etc
would never be available on Windows and that the LoadError would catch
it. Turns out that was an invalid assumption. This uses the safe
operator to gracefully handle it.

Fixes: 657cd71

Author: ekohl

lib/facter/root_home.rb

@@ -6,6 +6,6 @@
   rescue LoadError
   # Unavailable on platforms like Windows
   else
-    Etc.getpwnam('root').dir
+    Etc.getpwnam('root')&.dir
   end
 end