`heatmap(..., norm=None, ...)` has different behaviour than without specifying the `norm` argument

[stefanistrate]

Hi,

I'm noticing a strange behaviour when passing norm=None to a heatmap and I believe it's due to these lines:

seaborn/seaborn/matrix.py

Lines 299 to 303 in 3733590

	# setting vmin/vmax in addition to norm is deprecated
	# so avoid setting if norm is set
	if "norm" not in kws:
	kws.setdefault("vmin", self.vmin)
	kws.setdefault("vmax", self.vmax)

Specifically, if I use sns.heatmap(..., vmin=0.0, vmax=1.0, ...) I get something like this:

but when I use sns.heatmap(..., vmin=0.0, vmax=1.0, norm=None, ...), vmin and vmax are lost:

I'm happy to send a PR if this issue isn't addressed anywhere.

Ștefan