fix some warnings (#660)

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

examples/dom/size.cpp

@@ -7,7 +7,7 @@
 #include "ftxui/dom/node.hpp"      // for Render
 #include "ftxui/screen/color.hpp"  // for ftxui
 
-int main(int argc, const char* argv[]) {
+int main() {
   using namespace ftxui;
   auto make_box = [](const std::string& title) {
     return window(text(title) | hcenter | bold,