Don't crash when server is down

[ruuddotorg]

Response is undefined when the connection cannot be established, which
caused res.statusCode to blow up with:

/usr/src/app/node_modules/share2nightscout-bridge/index.js:238
        console.log("Error refreshing token", err, res.statusCode, body);
                                                      ^

TypeError: Cannot read property 'statusCode' of undefined

[ruuddotorg]

Verified that it now prints the following message but doesn't crash:

Error refreshing token { [Error: connect ETIMEDOUT 162.254.184.132:443]
  code: 'ETIMEDOUT',
  errno: 'ETIMEDOUT',
  syscall: 'connect',
  address: '162.254.184.132',
  port: 443 } undefined undefined

[PieterGit]

Fixed with #33