fix: TS types for the new name property (#331)

* fix: TS types for the new name property

* optional

* Revert "optional"

This reverts commit a012ca7.

Author: saihaj

.changeset/cyan-points-rescue.md

@@ -0,0 +1,5 @@
+---
+'dataloader': patch
+---
+
+`name` is an optional property

src/index.d.ts

@@ -123,7 +123,7 @@ declare namespace DataLoader {
      *
      * Is `null` if not set in the constructor.
      */
-    name: string | null;
+    name?: string | null;
   };
 }