docs: Fix example using the prove-block.sh

[mavroudisv]

The example uses a `native' proof type which is not the same as the curl call above and does not return a proof or quote.

The curl example uses: "prove": true which is passed as a parameter when using "$proof" == "sgx".

curl:

 curl --location 'http://localhost:8080' \
--header 'Content-Type: application/json' \
--data '{
    "proof_type": "sgx",
    "block_number": 99999,
    "prover": "0x7b399987d24fc5951f3e94a4cb16e87414bf2229",
    "graffiti": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "sgx": {
        **"setup": false,
        "bootstrap": false,
        "prove": true**
    }
}'

prove-block.sh:

if [ "$proof" == "native" ]; then
    proofParam='
    "proof_type": "native"
  '

...

elif [ "$proof" == "sgx" ]; then
    proofParam='
    "proof_type": "sgx",
    "sgx" : {
        "instance_id": 123,
        **"setup": false,
        "bootstrap": false,
        "prove": true,**
        "input_path": null
    }
    '