Specify node version used in package.json

backend/package.json

@@ -57,5 +57,8 @@
     "hooks": {
       "pre-commit": "npm test"
     }
+  },
+  "engines": {
+    "node": "12"
   }
 }

frontend/package.json

@@ -54,5 +54,8 @@
     "not dead",
     "not ie <= 11",
     "not op_mini all"
-  ]
+  ],
+  "engines": {
+    "node": "10"
+  }
 }