16c563b8966ad05c8c67450865cd26d7aa0436f5 Fix: Dropup wasn't working w…

…hen in an offset parent with a low position top

https://datatables.net/forums/discussion/79861

Sync to source repo @16c563b8966ad05c8c67450865cd26d7aa0436f5

datatables.json

@@ -14,5 +14,5 @@
     ],
     "src-repo": "http://github.com/DataTables/Buttons",
     "last-tag": "3.1.2",
-    "last-sync": "e4bc9e36c967a8db99affbe39d9f1144b25b6769"
+    "last-sync": "16c563b8966ad05c8c67450865cd26d7aa0436f5"
 }