usbstream: Wait for enter rather than infinite loop/sleep.

examples/usbstream/usbstream.cpp

@@ -1,6 +1,6 @@
 #include "cameraserver.h"
 
-#include <thread>
+#include <stdio.h>
 
 int main() {
   cs::USBCamera camera{"usbcam", 1};
@@ -8,5 +8,5 @@ int main() {
   cs::MJPEGServer mjpegServer{"httpserver", 8080};
   mjpegServer.SetSource(camera);
 
-  for (;;) std::this_thread::sleep_for(std::chrono::seconds(1));
+  getchar();
 }