fix: getTrendStats send {} to avoid axios stringify undefined

cfc-web/src/api/admin.js

@@ -437,7 +437,8 @@ export function getMembershipStats() {
 export function getTrendStats() {
   return request({
     url: '/api/stats/trend',
-    method: 'post'
+    method: 'post',
+    data: {}
   })
 }