Move towards resolving picture rendering bug

The bug concerns a mutable vector storing the amount of data that has
been poked.

src/ShapePicture.hs

@@ -40,7 +40,7 @@ noShape = (mempty :!:)
 
 overPosSP :: (Point3 -> Point3) -> SPic -> SPic
 {-# INLINE overPosSP #-}
-overPosSP f = bimap (overPosSH f) (picMap $ overPos f)
+overPosSP f = bimap (overPosSH f) (fmap $ overPos f)
 
 translateSPxy :: Float -> Float -> SPic -> SPic
 {-# INLINE translateSPxy #-}