bug in non-local block codes

[hezw2016]

Hey Author,

the original version in your repo:
def forward(self, x):
# [N, C, H, W]
b, c, h, w = x.size()
# [N, C/2, H * W]
x_phi = self.conv_phi(x).view(b, c, -1)

I guess it should be revised to:
x_phi = self.conv_phi(x).view(b, c//2, -1)

Best,
Zewei