fix some warnings (#660)

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

examples/dom/style_gallery.cpp

@@ -5,7 +5,7 @@
 #include "ftxui/dom/node.hpp"      // for Render
 #include "ftxui/screen/color.hpp"  // for Color, Color::Blue, ftxui
 
-int main(int argc, const char* argv[]) {
+int main() {
   using namespace ftxui;
   // clang-format off
   auto document =