Implementation of Shampoo inconsistent with the paper

[siddharth9820]

pytorch-optimizer/torch_optimizer/shampoo.py

Line 130 in 910b414

inv_precond.copy_(_matrix_power(precond, -1 / order))

Shouldn't the second argument be -0.5/order? For example, with order 2, the authors raise the precondition matrices to the -1/4th power.