add popper.js

public/vendor/popper.js/packages/popper/src/utils/getRoot.js

@@ -0,0 +1,14 @@
+/**
+ * Finds the root node (document, shadowDOM root) of the given element
+ * @method
+ * @memberof Popper.Utils
+ * @argument {Element} node
+ * @returns {Element} root node
+ */
+export default function getRoot(node) {
+  if (node.parentNode !== null) {
+    return getRoot(node.parentNode);
+  }
+
+  return node;
+}