Fixed typo

app/login.js

@@ -53,7 +53,7 @@ function writeUser(user, hash) {
 
 async function signup(user, pass) {
     if (user.length < 2 || user.length > 20)
-        return {"code": 400, "error": "Username should be 2-16 characters"};
+        return {"code": 400, "error": "Username should be 2-20 characters"};
     if (pass.length < 8 || pass.length > 32)
         return {"code": 400, "error": "Password should be 8-32 characters"};
     if (userExists(user))