[FIX] payment: transaction formview display issue

Using group without defining the col attribute will let the form
renderer choose the right display to avoid screwing up the layout

addons/payment/views/payment_acquirer.xml

@@ -99,7 +99,7 @@
             <field name="arch" type="xml">
                 <form string="Payment Transactions" version="7.0">
                     <sheet>
-                        <group col="6">
+                        <group>
                             <group>
                                 <field name="reference"/>
                                 <field name="amount"/>