feat(widget-relation): string templates support (#3659)

packages/netlify-cms-core/src/reducers/collections.ts

@@ -14,10 +14,12 @@ import {
   EntryMap,
 } from '../types/redux';
 import { selectMediaFolder } from './entries';
-import { keyToPathArray } from '../lib/stringTemplate';
+import { stringTemplate } from 'netlify-cms-lib-widgets';
 import { summaryFormatter } from '../lib/formatters';
 import { Backend } from '../backend';
 
+const { keyToPathArray } = stringTemplate;
+
 const collections = (state = null, action: CollectionsAction) => {
   switch (action.type) {
     case CONFIG_SUCCESS: {