Merge pull request #3142 from bluong/master

d3.select() has a behavior for no args

d3/d3.d.ts

@@ -9,6 +9,10 @@ declare module D3 {
         * Select an element from the current document
         */
         select: {
+            /**
+            * Returns the empty selection
+            */
+            (): Selection;
             /**
             * Selects the first element that matches the specified selector string
             *