fix check for shred PIDs

shredder.sh

@@ -44,7 +44,9 @@ done
 
 while true; do
   for child in ${children}; do
-    activeChildren="${activeChildren} $(ps T | grep $child | awk '{print $1}')"
+    if kill -0 ${child}; then
+      activeChildren="${activeChildren} ${child}"
+    fi
   done
 
   # if no active children, trim the whitespace so we can check for empty string