[IMP] pos_mercury: turn mercury_invoice_no into a char field
[IMP] pos_mercury: turn mercury_invoice_no into a char field

See 48eb674a7003f046207485cc127e314c0936313a.

ygol/odoo,ygol/odoo,hip-odoo/odoo,ygol/odoo,dfang/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,dfang/odoo,hip-odoo/odoo,hip-odoo/odoo,dfang/odoo,hip-odoo/odoo,dfang/odoo,hip-odoo/odoo,dfang/odoo