copy.deepcopy os.environ instead of copy

[NihalHarish]

Fixes: #2115

• bug fix: using envrion.copy() returns a dict.
• using deepcopy(environ) returns an _environ object
• Changing the datatype of the _environ object can break code, if subsequent libraries perform operations using apis exclusive to the environ object, like environ.getenv() for example.

Testing:

Tested the change on my terminal:

>>> import os
>>> x = deepcopy(os.environ)
>>> y = os.environ
>>> x is y
False
>>> isinstance(x, type(os.environ))
True
>>> z = os.environ.copy()
>>> isinstance(z, type(os.environ))
False
>>> isinstance(z, dict)
True

[lhoestq]

Good catch !
thank you