Update pytorch version when TLS issue is solved

[jrapin]

We observe incompatibility between pytorch 1.3.0 and sklearn:

(venv) circleci@95c3075fe681:~/repo$ python -m nevergrad.functions.rl.test_envs
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/runpy.py", line 183, in _run_module_as_main
    mod_name, mod_spec, code = _get_module_details(mod_name, _Error)
  File "/usr/local/lib/python3.6/runpy.py", line 109, in _get_module_details
    __import__(pkg_name)
  File "/home/circleci/repo/nevergrad/functions/rl/__init__.py", line 7, in <module>
    from . import agents
  File "/home/circleci/repo/nevergrad/functions/rl/agents.py", line 12, in <module>
    import torch
  File "/home/circleci/repo/venv/lib/python3.6/site-packages/torch/__init__.py", line 81, in <module>
    from torch._C import *
ImportError: dlopen: cannot load any more object with static TLS

A fix on pytorch may be coming:
pytorch/pytorch#28536

In the meantime version of pytorch is <1.3.0 (from #307)

[jrapin]

Solved by #391