resolve backward compatibility issues

Signed-off-by: Beichi-CHs <g841734459@126.com>

.travis.yml

@@ -5,7 +5,6 @@ services:
     - docker
     - postgresql
 install:
-    - pip install psycopg2
     - pip install -r deploy/requirements.txt
     - echo `cat /dev/urandom | head -1 | md5sum | head -c 32` > data/config/secret.key
     - ./init_db.sh
@@ -15,6 +14,4 @@ script:
     - coverage run --include="$PWD/*" manage.py test
     - coverage report
 notifications:
-    email:
-        - beichi.dev@gmail.com
-        - 841734459@qq.com
+    slack: onlinejudgeteam:BzBz8UFgmS5crpiblof17K2W

docs/data.json

@@ -1,5 +1,14 @@
 {
   "update": [
+    {
+      "version": "2021-11-20",
+      "level": "Important",
+      "title": "2021-11-20",
+      "details": [
+        "django2.x即将停止支持，更新django到3.x LTS，相应地更新了全部相关依赖",
+        "合并底包版本到python3.8-alpine3.14，为移除python2做准备"
+      ]
+    },
     {
       "version": "2021-09-28",
       "level": "Recommend",

oj/settings.py

@@ -244,3 +244,5 @@ RAVEN_CONFIG = {
 }
 
 IP_HEADER = "HTTP_X_REAL_IP"
+
+DEFAULT_AUTO_FIELD='django.db.models.AutoField'

utils/models.py

@@ -1,4 +1,4 @@
-from django.contrib.postgres.fields import JSONField  # NOQA
+from django.db.models import JSONField  # NOQA
 from django.db import models
 
 from utils.xss_filter import XSSHtml