离线考试：文件名后缀必须是小写

src/features/OfflineExam/OfflineExamUpload.vue

@@ -200,6 +200,15 @@ export default {
       });
     },
     handleBeforeUpload(file) {
+      const suffix = file.name.split(".").pop();
+      if (suffix.toLowerCase() !== suffix) {
+        this.$Notice.error({
+          title: "文件名后缀必须是小写",
+          desc: file.name + " 文件名后缀必须是小写。"
+        });
+        return Promise.reject("file suffix should be lower case");
+      }
+
       return new Promise((resolve, reject) => {
         this.$Modal.confirm({
           title: "已有作答附件，是否覆盖？",