Update .nvmrc to a working version

[Joe0]

.nvmrc version is too old and when using the version specified the project will not run.

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[bobiechen-twilio]

Hi @Joe0

Could you please share any error/warning or more information when the project failed to run?

Thanks -bobie

[Joe0]

Error:

$ node .
./voice-quickstart-server-node/src/server.js:99
async function placeCall(request, response) {
      ^^^^^^^^
SyntaxError: Unexpected token function
    at createScript (vm.js:56:10)
    at Object.runInThisContext (vm.js:97:10)
    at Module._compile (module.js:542:28)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.require (module.js:497:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (./voice-quickstart-server-node/index.js:7:17)

async function placeCall(request, response) is causing an error, because node v6.10.2 doesn't support async/await. Using a more modern version of node solves the problem, so I just bumped the version specified in the .nvmrc.

I just realized that the change should also be reflected in the package.json. I'll amend the PR to reflect that.

[charliesantos]

Thanks @Joe0 , this looks good. Merging..