Set correct content type to json

ao3-subscribe.user.js

@@ -95,7 +95,7 @@ async function loginToTinyTinyRSS() {
     const loginResponse = await fetch("https://news.nas.franpenedo.com/api/", {
         method: "POST",
         headers: {
-            "Content-Type": "application/x-www-form-urlencoded",
+            "Content-Type": "application/json",
         },
         body: JSON.stringify({ op: "login", user: creds.usr, password: creds.pword }),
     });
@@ -114,7 +114,7 @@ async function subscribeToFeed(feedURL, sessionID) {
     const subscribeResponse = await fetch("https://news.nas.franpenedo.com/api/", {
         method: "POST",
         headers: {
-            "Content-Type": "application/x-www-form-urlencoded",
+            "Content-Type": "application/json",
         },
         body: JSON.stringify({ op: "subscribeToFeed", feed_url: feedURL, category_id: 11, sid: sessionID }),
     });