Fix typo

src/sysinfo.rs

@@ -101,6 +101,6 @@ fn do_show_system(writer: &mut dyn io::Write, fs: &dyn procfsapi::ProcfsAPI, tim
     Ok(())
 }
 
-// Currently the test for do_show_system() is whitebox, see ../tests.  The reason for this is partly
+// Currently the test for do_show_system() is black-box, see ../tests.  The reason for this is partly
 // that not all the system interfaces used by that function are virtualized at this time, and partly
 // that we only care that the output syntax looks right.