dataclasses dependency

Summary:
Pull Request resolved: #2651

Pull Request resolved: facebookresearch/fvcore#57

close facebookresearch/fvcore#56

Reviewed By: theschnitz

Differential Revision: D26585142

fbshipit-source-id: 321bb84406a78fc0cebbe49b1f9329087c48bd4f

Author: ppwwyyxx

setup.py

@@ -216,6 +216,7 @@ def get_model_zoo_configs() -> List[str]:
         "pycocotools>=2.0.2",  # corresponds to https://github.com/ppwwyyxx/cocoapi
         "future",  # used by caffe2
         "pydot",  # used to save caffe2 SVGs
+        "dataclasses; python_version<'3.7'",
     ],
     extras_require={
         "all": [