Cannot extract Amazon Rating

Describe the problem.
I am using the sample json to extract Amazon Reviews:

The output for rating is: 4.2 out of 5 Stars. I want to extract 4.2 only and I used the regex shown below.
However when I import the sitemap, I get an invalid message: Invalid JSON.

Why is that so?

The Sitemap:
{
"id": "rating",
"type": "SelectorText",
"parentSelectors": [
"review"
],
"selector": "span.a-icon-alt",
"multiple": false,
"regex": "([^\s]+)",
"delay": 0
},

This will work for the example Url. The regex is: .+(?= out of)

Sitemap:
{"_id":"forum-amazon-rating","startUrl":["https://www.amazon.com/Screen-Protector-SPARIN-Tempered-Glass/product-reviews/B013JZCAZK/ref=cm_cr_dp_d_show_all_btm?ie=UTF8&reviewerType=all_reviews"],"selectors":[{"id":"Item name","type":"SelectorText","parentSelectors":["_root"],"selector":"div[class*='title'] h1.a-size-large","multiple":false,"regex":"","delay":0},{"id":"Reivew","type":"SelectorText","parentSelectors":["_root"],"selector":"div > span[data-hook^='rating']","multiple":false,"regex":".+(?= out of)","delay":0}]}