Add TypeFamilies extension to Linear.Matrix

This fixes one of several build errors when compiling with GHC HEAD.

    src/Linear/Matrix.hs:65:4:
        Illegal equational constraint Rep f ~ Rep f
        (Use GADTs or TypeFamilies to permit this)
        When checking that ‘o’ has the inferred type
          o :: forall (f1 :: * -> *) (f2 :: * -> *).
               (Representable f2, Representable f1, Rep f2 ~ Rep f,
                Rep f1 ~ Rep f) =>
               f2 b -> f1 t
        In an equation for ‘column’:
            column l f es
              = o <$> f i
              where
                  go = l (Context id)
                  i = tabulate $ \ e -> ipos $ go (index es e)
                  o eb = tabulate $ \ e -> ipeek (index eb e) (go (index es e))