课堂列表调整

app/views/courses/mine.json.jbuilder

@@ -1,5 +1,6 @@
 json.partial! "commons/success"
-json.data do
-  json.array! @courses, :id, :name, :updated_at, :created_at, :end_date
+json.data @courses do |course|
+  json.(course, :id, :name, :updated_at, :end_date)
+  json.created_at course.created_at.strftime("%Y-%m-%d")
 end