Unable to pickle typing.Dict[kt, vt] and List[vt] on python 3.6

[pereman2]

Describe the bug
Pickling generic types Dict[kt, vt] and List[vt]on python 3.6 produces an error.

To Reproduce

@dataclass
class Pick:
    union: Dict[str, int] = field(default_factory=lambda: {})

with tempfile.TemporaryFile() as fp:
    c = OmegaConf.structured(Pick)
    pickle.dump(c, fp)
    fp.flush()
    fp.seek(0)
    c1 = pickle.load(fp)

Expected behavior
It should be able to pickle.

Additional context

• OmegaConf version: 2.1.0
• Python version: 3.6
• Operating system : macOS
• Please provide a minimal repro

[omry]

@JieruHu, this could be related to the issue you are seeing in the Ray Launcher on 3.6.