React App Example Throws Error (SharedArrayBuffer is not defined)

**Describe the bug**
A clear and concise description of what the bug is.

**To Reproduce**
Steps to reproduce the behavior:
1. Clone the repo
2. Install dependencies (yarn)
3. Run app (yarn start)
4. Open http://localhost:300
5. Click "Start"
6. You will see an error like:
```
Unhandled Rejection (ReferenceError): SharedArrayBuffer is not defined
▶ 2 stack frames were collapsed.
async doTranscode
src/App.js:13
10 | });
11 | const doTranscode = async () => {
12 | setMessage('Loading ffmpeg-core.js');
> 13 | await ffmpeg.load();
| ^ 14 | setMessage('Start transcoding');
15 | ffmpeg.FS('writeFile', 'test.avi', await fetchFile('/flame.avi'));
16 | await ffmpeg.run('-i', 'test.avi', 'test.mp4');
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```

**Expected behavior**
Of course, the demo working fresh from an install to work.

**Screenshots**

**Desktop (please complete the following information):**
- OS: macOS 11.4
- Browser Chrome
- Version 92.0.4515.131 (Official Build) (x86_64)