PayFlow: focus on cancel button on modal open

src/PayFlow.svelte

@@ -83,9 +83,11 @@
     isOpen=false
   }
 
+  let cancelButton;
+
 </script>
 
-<Modal {isOpen} toggle={dismiss} size='lg'>
+<Modal {isOpen} toggle={dismiss} on:open={()=>cancelButton.focus()} size='lg'>
   <ModalHeader>BOLT11 invoice: {stage}</ModalHeader>
   <ModalBody>
     {#if confirmAmount}
@@ -158,6 +160,7 @@
       {/if}
       <button
 	class="btn btn-outline-primary"
+	bind:this={cancelButton}
 	type="button" on:click="{dismiss}">Cancel</button>
     </div>
   </ModalFooter>