Don't use deprecated QRegularExpression option

The following is the warning from compiler:
rss_item.cpp:70:79: warning: ‘QRegularExpression::OptimizeOnFirstUsageOption’ is deprecated: This option does not have any effect since Qt 5.12 [-Wdeprecated-declarations]

src/base/rss/rss_item.cpp

@@ -67,7 +67,7 @@ bool Item::isValidPath(const QString &path)
 {
     static const QRegularExpression re(
                 QString(R"(\A[^\%1]+(\%1[^\%1]+)*\z)").arg(Item::PathSeparator)
-                , QRegularExpression::DontCaptureOption | QRegularExpression::OptimizeOnFirstUsageOption);
+                , QRegularExpression::DontCaptureOption);
 
     if (path.isEmpty() || !re.match(path).hasMatch()) {
         qDebug() << "Incorrect RSS Item path:" << path;