Moved y2018 Drivetrain Writer.

Just another refactoring step.

Change-Id: I70799c0db8722bbab632580b93aadb6f333417ae
diff --git a/y2018/BUILD b/y2018/BUILD
index 1fc9d1b..18a8ba0 100644
--- a/y2018/BUILD
+++ b/y2018/BUILD
@@ -87,6 +87,7 @@
         "//frc971/wpilib:buffered_pcm",
         "//frc971/wpilib:dma",
         "//frc971/wpilib:dma_edge_counting",
+        "//frc971/wpilib:drivetrain_writer",
         "//frc971/wpilib:encoder_and_potentiometer",
         "//frc971/wpilib:joystick_sender",
         "//frc971/wpilib:logging_queue",