Rename ol.Observable#dispatchChangeEvent() to #changed()

Since dispatchChangeEvent does not only dispatch a change event, but
also increases the revision counter, the method name should reflect
this.

src/ol/source/imagemapguidesource.js

@@ -179,7 +179,7 @@ ol.source.ImageMapGuide.getScale = function(extent, size, metersPerUnit, dpi) {
  */
 ol.source.ImageMapGuide.prototype.updateParams = function(params) {
   goog.object.extend(this.params_, params);
-  this.dispatchChangeEvent();
+  this.changed();
 };