fix(util.typecoercedataset): restore timeline.itemsData.clear accessor (

#716)

* fix(util.typecoercedataset): restore timeline.itemsData.clear accessor

This bug was introduced in #259 , and constituted a breaking change.

This commit should fix #715.

* revert "fix(util.typecoercedataset): restore timeline.itemsData.clear accessor"

This reverts commit ba888c7.

lib/util.js

@@ -201,6 +201,7 @@ export function typeCoerceDataSet(
     remove: (...args) => rawDS.getDataSet().remove(...args),
     update: (...args) => rawDS.getDataSet().update(...args),
     updateOnly: (...args) => rawDS.getDataSet().updateOnly(...args),
+    clear : (...args) => rawDS.getDataSet().clear(...args),
 
     // Read only.
     forEach: coercedDS.forEach.bind(coercedDS),