improve the s3m lib

libs/s3m/S3MTiles/S3MTile.js

   }
 
   this.contentState = ContentState.LOADING
-  this.contentReadyPromise = Cesium.when.defer()
+  this.contentReadyPromise = new Promise()
   let contentFailedFunction = getContentFailedFunction(this)
 
   promise

libs/s3m/S3MTiles/S3MTilesLayer.js

     distance: Number.MAX_VALUE,
     pixel: Number.MAX_VALUE
   }
-  this._readyPromise = Cesium.when.defer()
+  this._readyPromise = new Promise()
 
   this.loadConfig(options.url)
 }
 
 S3MTilesLayer.prototype.loadConfig = function(url) {
   let that = this
-  Cesium.when(url)
+  Promise.resolve(url)
     .then(function(url) {
       let basePath
       let resource = Cesium.Resource.createIfNeeded(url)