fix: updating function aggregate to return int too

[manofstrong]

Running function count at the moment returns this fatal error:

string 'Medoo\Medoo::aggregate(): Return value must be of type ?string, int returned' 

This is caused by private function aggregate requiring a string return:

private function aggregate(string $type, string $table, $join = null, $column = null, $where = null): ?string

while public function count returns (and requires the return of ) an int type

public function count(string $table, $join = null, $column = null, $where = null): ?int
   {
        return (int) $this->aggregate('COUNT', $table, $join, $column, $where);
  }

my solution here is adding int return to private function aggregate

private function aggregate(string $type, string $table, $join = null, $column = null, $where = null): null|string|int