fixed asInteger math issue.

ZString.cpp

@@ -139,7 +139,7 @@ namespace coreutils {
 	return 0;
       while((*cursor >- '0') && (*cursor <= '9')) {
 	 value *= 10;
-	 value += *cursor - 40;
+	 value += *cursor - 48;
 	 ++cursor;
 	 if(cursor == end) {
 	    if(negative)