Subscriptions quotes nid, breaks in PostgreSQL.

The dev version of subscriptions 5.x-1.x-dev is selecting NIDs improperly, at least it breaks in PostgreSQL. Taxonomy does this right:

taxonomy/taxonomy.module:  db_query('DELETE FROM {term_node} WHERE nid = %d', $n
id);

But the subscriptions module is doing it wrong:

subscriptions/subscriptions.module:  $result = db_query('SELECT tid FROM {term_n
ode} WHERE nid = "%s"', $nid);

This patch fixes this by changing the latter to match the former, fixing the bug.