use deepmerge properly

src/mapviewer.js

@@ -5,8 +5,8 @@ import fetch from 'unfetch'               // To do Ajax requests with browser na
 import 'regenerator-runtime/runtime'      // To support async polyfill by babel
 import { scale } from './scale.js'
 import deepmerge from 'deepmerge'
-import deepclone from 'lodash/cloneDeep';
-import isPlainObject from "is-plain-object";
+import deepclone from 'lodash/cloneDeep'
+import isPlainObject from "is-plain-object"
 
 
 // To add to window
@@ -47,7 +47,7 @@ export var MapViewer = class MapViewer {
     self.mapDiv = typeof (self.options.id) === 'string' ? document.getElementById(self.options.id) : self.options.id
 
     // Apply defaults to the configuration
-    deepmerge(defaults, self.options, {
+    self.options = deepmerge(defaults, self.options, {
       isMergeableObject: isPlainObject
     })