fix the isNaN sanitizer in kill(..).

The `isNaN(..)` method returns a boolean, therefore the result of the `typeof isNaN(pid)` expression will always be `"boolean"`, therefore the condition in the if-statement is always truthy.  

The fix is simply to remove the `typeof`.

lib/cmd.js

@@ -40,7 +40,7 @@ module.exports = {
       throw new Error('PID is required for the kill operation.');
     }
 
-    if (typeof isNaN(pid)) {
+    if (isNaN(pid)) {
       throw new Error('PID must be a number.')
     }
 
@@ -86,4 +86,4 @@ module.exports = {
     });
   }
 
-};
+};