fix jest

packages/hydrooj/package.json

@@ -33,7 +33,6 @@
         "markdown-it-table-of-contents": "^0.4.4",
         "moment-timezone": "^0.5.31",
         "mongodb": "^3.5.9",
-        "mongodb-watcher": "^1.3.0",
         "nodemailer": "^6.4.10",
         "nunjucks": "^3.2.2",
         "prismjs": "^1.20.0",
@@ -71,4 +70,4 @@
         "build": "tsc",
         "build:watch": "tsc --watch"
     }
-}
+}