• I have reviewed the documentation
• I have searched existing issues
• I am using the latest React Native version

Fetch is no longer returning all rows of the same-name response headers! This only just happened after recent upgrade.

Environment

Environment:
OS: Windows 10
Node: 9.2.0
Yarn: 1.3.2
npm: 5.8.0
Watchman: Not Found
Xcode: N/A
Android Studio: Version 3.0.0.0 AI-171.4443003

Packages: (wanted => installed)
react: 16.3.1 => 16.3.1
react-native: ^0.55.3 => 0.55.3

Steps to Reproduce

Server returns the following response

return response()->json(['msg'=>'1'], 200)
->withHeaders(['Content-Type'=>'application/json', 't1'=>[1, 2]]);

** react native code **

let response = await fetch('http://im-sick-and-tired-of-hunting-react-native-bugs',
{
            credentials: 'include',
            method: 'GET',
            cache: 'no-cache',
            mode: 'cors',
            headers: {'Cache-Control': 'no-cache', 'Accept':'*/*', 'Content-Type':'application/json'},
});
console.log(response.headers.get('t1')); 

Expected Behavior

The test hdr (t1) must have both values but only the 2nd one is received. See the response from postman

Actual Behavior