JS Header  is not defined

When running js code, i got an error.

js code is below

```
var myHeaders = new Headers();
myHeaders.append("Content-Type", "application/json");
```

error is below

```
unhandled promise rejection: ReferenceError: 'Headers' is not defined
    at webhook (<eval>:2)
    at <eval> (<eval>:32)
```
