fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/npm:braces:20180219

Author: snyk-test

package.json

@@ -32,7 +32,7 @@
     "mongoose": "^5.1.7",
     "muicss": "^0.9.39",
     "multer": "^1.3.0",
-    "next": "^6.0.3",
+    "next": "^7.0.0",
     "passport": "^0.4.0",
     "passport-local": "^1.0.0",
     "pm2": "^3.2.1",