Use upstream Blob directly in typings (#38)

index.d.ts

@@ -1,18 +1,4 @@
 /// <reference lib="dom"/>
 
-/** A file-like object of immutable, raw data. Blobs represent data that isn't necessarily in a JavaScript-native format. The File interface is based on Blob, inheriting blob functionality and expanding it to support files on the user's system. */
-declare interface FetchBlob extends Blob {
-	[Symbol.toStringTag]: 'Blob';
-	stream: () => ReadableStream;
-	text: () => Promise<string>;
-	arrayBuffer: () => Promise<ArrayBuffer>;
-	toString: () => '[object Blob]';
-
-}
-
-declare const FetchBlob: {
-	prototype: FetchBlob;
-	new(blobParts?: BlobPart[], options?: BlobPropertyBag): FetchBlob;
-};
-
-export = FetchBlob;
+/* global Blob */
+export = Blob;