chore: bump vue-jest to support babel@7

Author: ulivz

packages/@vuepress/test-utils/package.json

@@ -29,7 +29,7 @@
     "execa": "^0.10.0",
     "jest-serializer-vue": "^1.0.0",
     "ts-jest": "^23.10.5",
-    "vue-jest": "^3.0.3"
+    "vue-jest": "^4.0.0-beta.1"
   },
   "author": "ULIVZ <chl814@foxmail.com>",
   "license": "MIT",