48399b8f822f40cde08e0b56a0a84b70e8c6a678 Fix: Add attr option to button typing

https://datatables.net/forums/discussion/75475

Sync to source repo @48399b8f822f40cde08e0b56a0a84b70e8c6a678

Author: AllanJard

datatables.json

@@ -15,5 +15,5 @@
     ],
     "src-repo": "http://github.com/DataTables/Buttons",
     "last-tag": "2.3.4",
-    "last-sync": "30575e1db8a1d327908215f9952ce8ab35e3101a"
+    "last-sync": "48399b8f822f40cde08e0b56a0a84b70e8c6a678"
 }

types/types.d.ts

@@ -385,6 +385,13 @@ declare module 'datatables.net' {
 		 */
 		action?: FunctionButtonAction;
 
+		/**
+		 * Button HTML attributes
+		 */
+		attr?: {
+			[key: string]: string | number
+		};
+
 		/**
 		 * Ensure that any requirements have been satisfied before initialising a button
 		 */