invalid JSON RPC response

I Just cloned the repo and try to lunch the verifier but I have this issue:

$ node index.js -a 0x1234...FFFF -c 0x37dC71366Ec655093b9930bc816E16e6b587F968
Error: Invalid JSON RPC response: ""
    at Object.InvalidResponse (/Users/nicolasburtey/Projects/livepeer/verification-computation-solver/node_modules/web3/lib/web3/errors.js:38:16)
    at XMLHttpRequest.request.onreadystatechange (/Users/nicolasburtey/Projects/livepeer/verification-computation-solver/node_modules/web3/lib/web3/httpprovider.js:116:24)
    at XMLHttpRequestEventTarget.dispatchEvent (/Users/nicolasburtey/Projects/livepeer/verification-computation-solver/node_modules/xhr2/lib/xhr2.js:64:18)
    at XMLHttpRequest._setReadyState (/Users/nicolasburtey/Projects/livepeer/verification-computation-solver/node_modules/xhr2/lib/xhr2.js:354:12)
    at XMLHttpRequest._onHttpRequestError (/Users/nicolasburtey/Projects/livepeer/verification-computation-solver/node_modules/xhr2/lib/xhr2.js:544:12)
    at ClientRequest.<anonymous> (/Users/nicolasburtey/Projects/livepeer/verification-computation-solver/node_modules/xhr2/lib/xhr2.js:414:24)
    at ClientRequest.emit (events.js:127:13)
    at Socket.socketErrorListener (_http_client.js:394:9)
    at Socket.emit (events.js:127:13)
    at emitErrorNT (internal/streams/destroy.js:64:8)

Start with index.js and reproduce the documented node index.js command. Trace how the verifier configures its JSON-RPC provider and compare that with the reported Web3 invalid-response stack trace. Done means the verifier starts successfully and receives a valid JSON-RPC response.