fixup! feat: expose codec code and allow construction by code

Author: rvagg

src/index.js.flow

@@ -14,7 +14,7 @@ declare class CID<a> {
   constructor(Uint8Array): void;
 
   +codec: Codec;
-	+code: CodecCode;
+  +code: CodecCode;
   +multihash: Multihash;
   +bytes: Uint8Array;
   +prefix: Uint8Array;