Update README.md

code block error

Author: Sam-Bieberich

MxNet/Classification/RN50v1.5/README.md

@@ -220,7 +220,7 @@ nvidia-docker run --rm -it --ipc=host -v <path to dataset>:/data/imagenet/train-
     find . -name "*.tar" | while read NAME ; do mkdir -p "${NAME%.tar}"; tar -xvf "${NAME}" -C "${NAME%.tar}"; rm -f "${NAME}"; done
     cd ..
     mkdir val && mv ILSVRC2012_img_val.tar val/ && cd val && tar -xvf      ILSVRC2012_img_val.tar
-wget -qO- https://raw.githubusercontent.com/soumith/imagenetloader.torch/master/valprep.sh | bash
+    wget -qO- https://raw.githubusercontent.com/soumith/imagenetloader.torch/master/valprep.sh | bash
     ```
 
 5. Preprocess the ImageNet 1k dataset.