Fix ordering between CameraServer.getInstance and UsbCamera creation (#69)

If the CameraServer instance is started after the UsbCamer is created, it
never gets the source created event to actually build the NetworkTable table.

deps/examples/cpp-multiCameraServer/main.cpp

@@ -170,8 +170,8 @@ bool ReadConfig() {
 cs::UsbCamera StartCamera(const CameraConfig& config) {
   wpi::outs() << "Starting camera '" << config.name << "' on " << config.path
               << '\n';
-  cs::UsbCamera camera{config.name, config.path};
   auto inst = frc::CameraServer::GetInstance();
+  cs::UsbCamera camera{config.name, config.path};
   auto server = inst->StartAutomaticCapture(camera);
 
   camera.SetConfigJson(config.config);