Add epsilon on variance of batch normalization layer.

[Corea]

caffe (https://github.com/BVLC/caffe/blob/master/src/caffe/layers/batch_norm_layer.cpp#L150) and Tensorflow (https://github.com/tensorflow/tensorflow/blob/754048a0453a04a761e112ae5d99c149eb9910dd/tensorflow/core/kernels/batch_norm_op.h#L117) add epsilon value to variance.

[nihui]

epsilon has been added during caffe2ncnn, see

ncnn/tools/caffe2ncnn.cpp

Line 440 in 5b9a198

tmp = var_blob.data().data()[j] + eps;

[Corea]

Sorry, I didn't check caffe2ncnn code. Then I will add some code to process FusedBatchNorm on tensorflow2ncnn, and also put similar code on them. thanks!