Fix circular dependency compile error.

Author: ehsannas

packages/firestore/src/local/local_documents_view.ts

@@ -15,14 +15,14 @@
  * limitations under the License.
  */
 
-import { Timestamp } from '../api';
 import {
   asCollectionQueryAtPath,
   isCollectionGroupQuery,
   isDocumentQuery,
   Query,
   queryMatches
 } from '../core/query';
+import { Timestamp } from '../lite-api/timestamp';
 import {
   documentKeySet,
   DocumentKeySet,