fix: fixed export of APIChainOptions (#1410)

* fix: fixed export of APIChainOptions

* Formatting

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Co-authored-by: Vijay Sai <vijaysaijnv@gamil.com>
Co-authored-by: Jacob Lee <jacoblee93@gmail.com>

langchain/src/chains/index.ts

@@ -1,6 +1,6 @@
 export { BaseChain, ChainInputs } from "./base.js";
 export { LLMChain, LLMChainInput } from "./llm_chain.js";
-export { APIChain, APIChainInput } from "./api/api_chain.js";
+export { APIChain, APIChainInput, APIChainOptions } from "./api/api_chain.js";
 export { ConversationChain } from "./conversation.js";
 export {
   SequentialChain,