Discriminated union example fails to parse (#1713)

https://zod.dev/?id=discriminated-unions

``` typescript
myUnion.parse({ type: "success", data: "yippie ki yay" });
```
→ ❌
``` json
    ZodError: [
      {
        "code": "invalid_union_discriminator",
        "options": [
          "success",
          "failed"
        ],
        "path": [
          "status"
        ],
        "message": "Invalid discriminator value. Expected 'success' | 'failed'"
      }
    ]
```

``` typescript
myUnion.parse({ status: "success", data: "yippie ki yay" });
```
→ ✅

README.md

@@ -1294,7 +1294,7 @@ const myUnion = z.discriminatedUnion("status", [
   z.object({ status: z.literal("failed"), error: z.instanceof(Error) }),
 ]);
 
-myUnion.parse({ type: "success", data: "yippie ki yay" });
+myUnion.parse({ status: "success", data: "yippie ki yay" });
 ```
 
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