query-builder: Bind operand to where clause

query-builder: Bind operand to where clause

ex) AdminTable.select(Admin::Uid, Admin::Key).where(Admin::Id > 3);
  - Before: "SELECT uid, key FROM admin WHERE id > ?"
  - After: "SELECT uid, key FROM admin WHERE id > 3"

Signed-off-by: Sangwan Kwon <sangwan.kwon@samsung.com>