[BUG] Duplicate attributes fields when generating Python class docstrings

[peytondmurray]

Currently (as of d7f9461), neogen generates duplicate attributes for certain Python classes:

class Foo:
    def __init__(self, *args, **kwargs):
        self.app = None

    def bar(self, baz):
        self.app = baz

When I call require('neogen').generate(), I get:

class Foo:
    """

    Attributes
    ----------
    app : 
    app : 

    """
    def __init__(self, *args, **kwargs):
        self.app = None

    def bar(self, baz):
        self.app = baz

Here's my neovim version, in case it matters:

NVIM v0.12.0-dev-172+ged5e70465a
Build type: RelWithDebInfo
LuaJIT 2.1.1744317938