json middleware does not work on content types with a `+`

The json middleware does not parse results as json if the content type is anything but `application/json`, I would expect it to also work on content types like `application/ld+json`. For instance:

```ts
import express from 'express';
const app = express();
app.use(express.json());

app.post('/', async (req, res) => {
console.log("Data posted", await req.body);
});

app.listen(3000, () => {
console.log('Listening on port 3000');
fetch('http://localhost:3000', {
method: 'POST',
headers: {
'Content-Type': 'application/json',
},
body: JSON.stringify({
message: 'Hello world',
}),
});
});
```

returns

```
Listening on port 3000
Data posted { message: 'Hello world' }
```

On the other hand

```ts
import express from 'express';
const app = express();
app.use(express.json());

app.post('/', async (req, res) => {
console.log("Data posted", await req.body);
});

app.listen(3000, () => {
console.log('Listening on port 3000');
fetch('http://localhost:3000', {
method: 'POST',
headers: {
'Content-Type': 'application/ld+json',
},
body: JSON.stringify({
message: 'Hello world',
}),
});
});
```

returns

```
Listening on port 3000
Data posted {}
```