Replace boost::optional with std::optional (#4877)

src/providers/twitch/PubSubManager.cpp

@@ -727,14 +727,14 @@ void PubSub::registerNonce(QString nonce, NonceInfo info)
     this->nonces_[nonce] = std::move(info);
 }
 
-boost::optional<PubSub::NonceInfo> PubSub::findNonceInfo(QString nonce)
+std::optional<PubSub::NonceInfo> PubSub::findNonceInfo(QString nonce)
 {
     // TODO: This should also DELETE the nonceinfo from the map
     auto it = this->nonces_.find(nonce);
 
     if (it == this->nonces_.end())
     {
-        return boost::none;
+        return std::nullopt;
     }
 
     return it->second;