fix[Drag]: fixed drag bug in firefox (#1841)

src/components/Kanban/index.vue

@@ -7,6 +7,7 @@
       :list="list"
       v-bind="$attrs"
       class="board-column-content"
+      :set-data="setData"
     >
       <div v-for="element in list" :key="element.id" class="board-item">
         {{ element.name }} {{ element.id }}
@@ -39,6 +40,13 @@ export default {
         return []
       }
     }
+  },
+  methods: {
+    setData(dataTransfer) {
+      // to avoid Firefox bug
+      // Detail see : https://github.com/RubaXa/Sortable/issues/1012
+      dataTransfer.setData('Text', '')
+    }
   }
 }
 </script>