Accept simpler attributions in sources

src/ol/source/tilesource.js

@@ -5,7 +5,6 @@ goog.provide('ol.source.TileOptions');
 goog.require('goog.asserts');
 goog.require('ol.events.Event');
 goog.require('ol');
-goog.require('ol.Attribution');
 goog.require('ol.Extent');
 goog.require('ol.TileCache');
 goog.require('ol.TileRange');
@@ -18,7 +17,7 @@ goog.require('ol.tilegrid.TileGrid');
 
 
 /**
- * @typedef {{attributions: (Array.<ol.Attribution>|undefined),
+ * @typedef {{attributions: (olx.source.AttributionOption|undefined),
  *            cacheSize: (number|undefined),
  *            extent: (ol.Extent|undefined),
  *            logo: (string|olx.LogoOptions|undefined),