Add supporting themes required for Lotusdocs

themes/hugo-mod-jslibs-dist/popperjs/package/lib/utils/uniqueBy.js.flow

@@ -0,0 +1,14 @@
+// @flow
+
+export default function uniqueBy<T>(arr: Array<T>, fn: T => any): Array<T> {
+  const identifiers = new Set();
+
+  return arr.filter(item => {
+    const identifier = fn(item);
+
+    if (!identifiers.has(identifier)) {
+      identifiers.add(identifier);
+      return true;
+    }
+  });
+}