`nexmo account` should not fail if not logged in

[cbetta]

Current if the nexmo cli is not logged in the nexmo account command errors. This should probably be caught nicely.

➜  ~  nexmo account
fs.js:640
  return binding.open(pathModule._makeLong(path), stringToFlags(flags), mode);
                 ^

Error: ENOENT: no such file or directory, open '/Users/cbetta/.nexmorc'
    at Error (native)
    at Object.fs.openSync (fs.js:640:18)
    at Object.fs.readFileSync (fs.js:508:33)
    at Config.read (/Users/cbetta/.nvm/versions/node/v6.3.1/lib/node_modules/nexmo-cli/lib/config.js:31:47)
    at Request.accountInfo (/Users/cbetta/.nvm/versions/node/v6.3.1/lib/node_modules/nexmo-cli/lib/request.js:41:45)
    at Command.listener (/Users/cbetta/.nvm/versions/node/v6.3.1/lib/node_modules/nexmo-cli/node_modules/commander/index.js:301:8)
    at emitTwo (events.js:106:13)
    at Command.emit (events.js:191:7)
    at Command.parseArgs (/Users/cbetta/.nvm/versions/node/v6.3.1/lib/node_modules/nexmo-cli/node_modules/commander/index.js:615:12)
    at Command.parse (/Users/cbetta/.nvm/versions/node/v6.3.1/lib/node_modules/nexmo-cli/node_modules/commander/index.js:458:21)

[leggetter]

Closed via #94