Force the 4 point solution to contain the lowest point

Otherwise it may be optimal to have shorter targets.  This results in
significant skew which is bad.

Change-Id: I813d7977966afacec657cd6d2b86b225dfe6e169
diff --git a/aos/vision/math/vector.h b/aos/vision/math/vector.h
index 642c63f..5e7520f 100644
--- a/aos/vision/math/vector.h
+++ b/aos/vision/math/vector.h
@@ -91,6 +91,7 @@
   double Mag() const { return data_.norm(); }
 
   // Get underlying data structure
+  // TODO(austin): Everyone uses column not row vectors.
   ::Eigen::Matrix<double, 1, size> GetData() const { return data_; }
 
   // Set underlying data structure