[fixed] IE8 will now close an open DropdownButton menu when clicking button

This commit fixes an Internet Explorer 8 bug where attempting to close a button dropdown menu, by clicking the button itself, would not close the menu.
Event.target is undefined in IE8, so `isNodeInRoot(e.target, React.findDOMNode(this))` would return false, allowing the click event to bubble up to the document and re-open the menu.

Author: Will Hawker

Diff for: src/DropdownStateMixin.js

@@ -49,7 +49,9 @@ const DropdownStateMixin = {
   handleDocumentClick(e) {
     // If the click originated from within this component
     // don't do anything.
-    if (isNodeInRoot(e.target, React.findDOMNode(this))) {
+    // e.srcElement is required for IE8 as e.target is undefined
+    let target = e.target || e.srcElement;
+    if (isNodeInRoot(target, React.findDOMNode(this))) {
       return;
     }
 

Diff for: src/RootCloseWrapper.js

@@ -42,7 +42,9 @@ export default class RootCloseWrapper extends React.Component {
 
   handleDocumentClick(e) {
     // If the click originated from within this component, don't do anything.
-    if (isNodeInRoot(e.target, React.findDOMNode(this))) {
+    // e.srcElement is required for IE8 as e.target is undefined
+    let target = e.target || e.srcElement;
+    if (isNodeInRoot(target, React.findDOMNode(this))) {
       return;
     }