Pin omegaconf, as latest release conflicts with hydra-core

Summary:
Signed-off-by: Edward Z. Yang <[email protected]>

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Pull Request resolved: #5057

Reviewed By: shapovalov, r-barnes

Differential Revision: D48303938

Pulled By: ezyang

fbshipit-source-id: eedf6e79ce5d3a40b4ef6dca1c9ece22f00a9fa4

Author: ezyang

setup.py

@@ -186,7 +186,7 @@ def get_model_zoo_configs() -> List[str]:
         "fvcore>=0.1.5,<0.1.6",  # required like this to make it pip installable
         "iopath>=0.1.7,<0.1.10",
         "dataclasses; python_version<'3.7'",
-        "omegaconf>=2.1",
+        "omegaconf>=2.1,<2.4",
         "hydra-core>=1.1",
         "black",
         "packaging",