Before revision:  We estimate the value of p_c to be 0.4943 \pm 0.0005 and the critical exponent for the divergence of the correlation length \nu to be consistent with the 2D isotropic percolation value 4/3.
After revision:  We estimate the value of p_c = 0.49451 \pm 0.0005 and the critical exponent for the divergence of the correlation length \nu to be consistent with the 2D isotropic percolation value 4/3.