fix mistake in prismatic joint calculation

[fangnan99]

There is a mistake in the parallel Jacobian calculation for prismatic joints.

(Was mentioned in #3 but not fixed)

In jacobian.py, f.joint.axis.repeat(N, 1) result in shape (N,3) and cannot multiply with the (N,3,3) rotation matrix. Instead it should repeat(N,1,1) to get shape (N,1,3) to multiply with (N,3,3).

In frame.py, the expression theta * self.joint.axis is not permitted since the tensors have shapes (N,) and (3,). unsqueeze on theta solves it.