Update pytorch12

[juliendehos]

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Motivation and Context / Related issue

• fix tests
• fix compilation using pytorch 1.2
• handle pytorch version automatically (pytorch 1.5 and 1.2)

How Has This Been Tested (if it applies)

tested using Nix + pytorch 1.2

still to be done:

• test using pytorch 1.5
• clear caches in the CircleCI pipelines (still pytorch 1.1)

Checklist

• The documentation is up-to-date with the changes I made.
• I have read the CONTRIBUTING document and completed the CLA (see CONTRIBUTING).
• All tests passed, and additional code has been covered with new tests.