fix some warnings (#660)

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

examples/dom/style_color.cpp

@@ -6,7 +6,7 @@
 #include "ftxui/dom/node.hpp"      // for Render
 #include "ftxui/screen/color.hpp"  // for Color, operator""_rgb, Color::Black, Color::Blue, Color::BlueLight, Color::Cyan, Color::CyanLight, Color::DeepSkyBlue4, Color::Default, Color::GrayDark, Color::GrayLight, Color::Green, Color::GreenLight, Color::Magenta, Color::MagentaLight, Color::Red, Color::RedLight, Color::SkyBlue1, Color::White, Color::Yellow, Color::YellowLight, ftxui
 
-int main(int argc, const char* argv[]) {
+int main() {
   using namespace ftxui;
   auto document = hbox({
       vbox({