GitHub Apps with expiring tokens: The "expires_in" and "refresh_token_expires_in" keys in the JSON response for code exchange are numbers, not strings

tested with curl

```shell
curl -v -XPOST https://github.com/login/oauth/access_token -H"Accept: application/json" -H"Content-Type: application/json" -d '{"client_id": "Iv1.ee8d48b9ae654ff5", "client_secret": "[REDACTED]", "code": "519a7bfd9cb8ab6cfac2"}'
{"access_token":"[REDACTED]","expires_in":28800,"refresh_token":"[REDACTED]","refresh_token_expires_in":15897600,"token_type":"bearer","scope":""}
```

Author: gr2m

content/developers/apps/identifying-and-authorizing-users-for-github-apps.md

@@ -92,9 +92,9 @@ By default, the response takes the following form. The response parameters `expi
 ```json
 {
   "access_token": "e72e16c7e42f292c6912e7710c838347ae178b4a",
-  "expires_in": "28800",
+  "expires_in": 28800,
   "refresh_token": "r1.c1b4a2e77838347a7e420ce178f2e7c6912e1692",
-  "refresh_token_expires_in": "15811200",
+  "refresh_token_expires_in": 15811200,
   "scope": "",
   "token_type": "bearer"
 }