Fix issue with false selection detection

`selection.rangeCount` will return 1 when user is typing something in a
form widget. This will consequently trigger unvoluntary scrolling when
the mouse is moved outside of scrollable area. Checking the actual
length of selected text doesn't trigger this behaviour.

src/js/plugin/handler/selection.js

@@ -10,8 +10,8 @@ var h = require('../../lib/helper')
 function bindSelectionHandler(element, i) {
   function getRangeNode() {
     var selection = window.getSelection ? window.getSelection() :
-                    document.getSlection ? document.getSlection() : {rangeCount: 0};
-    if (selection.rangeCount === 0) {
+                    document.getSelection ? document.getSelection() : {rangeCount: 0};
+    if (selection.toString().length === 0) {
       return null;
     } else {
       return selection.getRangeAt(0).commonAncestorContainer;