update spring boot doc for config.js

[RealZimboGuy]

Hi,

please update the doc at https://github.com/NitorCreations/nflow/wiki/Spring-Boot-guide

the reference config.js file under #7 is in the old format and results in the below error

 var Config = function () {
  this.nflowUrl = 'http://localhost:8080/nflow/api';
  this.nflowApiDocs = 'http://localhost:8080/nflow/ui/doc/';
  this.radiator = {
    // poll period in seconds
    pollPeriod: 15,
    // max number of items to keep in memory
    maxHistorySize: 10000
  };
};

this should be in the new format, as per the below extract from the sample app https://github.com/NitorCreations/nflow/blob/master/nflow-examples/spring-boot/full-stack/maven/src/main/resources/static/explorer/config.js

var Config = new function() {
  this.refreshSeconds = 60;

  this.nflowEndpoints = [
    {
      id: 'localhost',
      title: 'local nflow instance',
      apiUrl: '/nflow/api',
      docUrl: '/nflow/ui/doc/'
    },
  ];
}

[RealZimboGuy]

also maybe reference that the startup url for explorer is as below without a /ui/

http://localhost:8080/explorer/index.html

[RealZimboGuy]

updated