Update simple-ls-ver2.c

Valgrind shows a memory leak related to the function call d = opendir(path) on line 50. Very much appreciate the book, btw. Helping me learn and
get comfortable with C!

kapitel11/simple-ls-ver2.c

@@ -62,6 +62,8 @@ int main(int argc, char **argv)
                 printf("%s\n", dir->d_name);
         }
     }
+    
+    closedir(d);
     return 0;
 }