Update all examples to latest versions of pytorch

[msaroufim]

Our RPC examples use an older version of PyTorch

grep -r "torch=" .
./distributed/rpc/pipeline/requirements.txt:torch==1.6.0
./distributed/rpc/batch/requirements.txt:torch==1.6.0

There could be others

[veekaybee]

I'd like to take this. Just to clarify, we should update all requirements files (starting with here, to torch==1.9.0.

I did a quick check of

find . -name '*requirements.txt' -exec grep -i 'torch' {} \; -print

and it looks like there are others that use torch but don't pin a version. Does it make sense to pin all of them and then do some kind of automated CI/CD check? Maybe that's phase 2 or 3. :)