Fix: lynqchat-jsのリクエストヘッダーにContent-Typeを追加

packages/lynqchat-js/src/index.ts

@@ -57,6 +57,9 @@ export default class LynqChat<
       {
         method: "POST",
         cache: "no-store",
+        headers: {
+          "Content-Type": "application/json",
+        },
         body,
       }
     );