Fix a typo in contribution doc (#604)

Co-authored-by: Xiao Tianci <xiaotianci1@huawei.com>

Author: TianciXiao

CONTRIBUTING.md

@@ -30,7 +30,7 @@ Start by installing the **nightly** build of PyTorch following the
 Then, the easiest way to install the rest of the dependencies is to run:
 
 ```bash
-conda install cmake pkg-config pbyind11 ffmpeg -c conda-forge
+conda install cmake pkg-config pybind11 ffmpeg -c conda-forge
 ```
 
 ### Clone and build