message: Fix incorrect operator in sub_assign impl
diff: @@ -205,7 +205,7 @@ macro_rules! impl_point {
  fn add_assign(&mut self, vector) { $(self.$field += vector.$field);+ }
  });
  impl_assignment_operator!(<S: BaseNum> SubAssign<$VectorN<S>> for $PointN<S> {
  - fn sub_assign(&mut self, vector) { $(self.$field += vector.$field);+ }
  + fn sub_assign(&mut self, vector) { $(self.$field -= vector.$field);+ }
  });
  impl_operator!(<S: BaseNum> Sub<$PointN<S> > for $PointN<S> {
  