Grammatically updated the tech docs (#41031)
Summary:
Small grammatical update to the torch tech docs
![image](https://user-images.githubusercontent.com/26879385/86633690-e126c400-bfc8-11ea-8892-23cdc037daa9.png)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41031
Differential Revision: D22404342
Pulled By: ngimel
fbshipit-source-id: 1c723119cfb050c4ef53de7971fe6e0acf3e91a9