Change fname to path in to_parquet

- [X] closes #23574
- [N/A ] tests added / passed
- [X ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ N/A?] whatsnew entry

https://github.com/pandas-dev/pandas/issues/23574
@WillAyd 

Ok!

I see other functions in this file use `deprecate_kwarg`

Looking at decorators:

https://github.com/pandas-dev/pandas/blob/master/pandas/util/_decorators.py#L78

I only see one for deprecating functions and keyword arguments.

Should I just do `@deprecate_kwarg(old_arg_name='fname', new_arg_name='path')` ?

Or should I just add  a deprecated comment in the functiondocstring? I think you’ll need to do both. If you look at past PRs labeled Deprecate could give you an idea of what to do

> On Apr 3, 2019, at 10:52 AM, ssikdar1 <notifications@github.com> wrote:
> 
> @WillAyd <https://github.com/WillAyd>
> Ok!
> 
> I see other functions in this file use deprecate_kwarg
> 
> Looking at decorators:
> 
> https://github.com/pandas-dev/pandas/blob/master/pandas/util/_decorators.py#L78 <https://github.com/pandas-dev/pandas/blob/master/pandas/util/_decorators.py#L78>
> I only see one for deprecating functions and keyword arguments.
> 
> Should I just do @deprecate_kwarg(old_arg_name='fname', new_arg_name='path') ?
> 
> Or should I just add a deprecated comment in the functiondocstring?
> 
> —
> You are receiving this because you were mentioned.
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> 

William Ayd
william.ayd@icloud.com



 this is even more complicated. we have a number of ``to_*`` methods. *most* use ``fname``, but some like ``to_csv`` use ``path_or_buf``.

So i think we actually need to decide a common arg and then *possibly* deprecate these Makes sense - @ssikdar1 I think in light of that this needs a little more discussion, so going to close out this PR because we should agree on approach first.

Do you have a point of view on how to tackle and if so could you post that to the original issue to lead that discussion? That would be the most constructive way to go about this one