fix: default config for heading 3

Author: CSUwangj

examples/config.json

@@ -90,7 +90,7 @@
     {
       "名称": "reference",
       "英文字体": "Times New Roman",
-      "中文字体": "楷体_GB2312",
+      "中文字体": "黑体",
       "字体大小": "五号",
       "对齐方式": "左对齐",
       "录入大纲": false,