Add torch to requirements.txt in language-modeling (#12040)

* Add torch to requirements.txt in language-modeling

* Update examples/pytorch/language-modeling/requirements.txt
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

examples/pytorch/language-modeling/requirements.txt

+torch >= 1.3
 datasets >= 1.1.3
 sentencepiece != 0.1.92
 protobuf