Docstrings are not formatted properly

[VighneshKSP]

Operating system: Windows 10
Python version: 3.7.0
Black version: 18.6b4
Does also happen on master: Yes

Input:

def func():
  """
 abc
 """

output:

def func():
    """
 abc
 """

Supplied input had 2 spaces for the docstring's starting quote and 1 space for the content abc and ending quotes. After running black on the file, it had four spaces for the starting quote while the remaining where unaffected. As per the discussion #144, expectation is that this should be formatted as per PEP 257 guidelines.

[zsol]

#144 is not implemented yet. Until then, this behavior is expected (as black will use 4 spaces for indentation and will not change the contents of docstrings).