Minor correction of StyleFunction docs

src/ol/style/style.js

@@ -195,8 +195,8 @@ ol.style.Style.prototype.setZIndex = function(zIndex) {
 
 /**
  * A function that takes an {@link ol.Feature} and a `{number}` representing
- * the view's resolution. The function should return an array of
- * {@link ol.style.Style}. This way e.g. a vector layer can be styled.
+ * the view's resolution. The function should return a {@link ol.style.Style}
+ * or an array of them. This way e.g. a vector layer can be styled.
  *
  * @typedef {function((ol.Feature|ol.render.Feature), number):
  *     (ol.style.Style|Array.<ol.style.Style>)}