Fix chained assignment error

[NirOfir]

Fixes#303

[JosephSBoyle]

@jnothman bump-- just ran into the issue that this PR resolves

[redst4r]

same here!

[Mat314159]

Same.
To "fix" it :
I git clone the code.
I modified it myself :
cd UpSetPlot/
mv upsetplot local_upsetplot
cd local_upsetplot

I modified plotting.py lines 795-798. Replace those lines by :

styles["linewidth"] = styles["linewidth"].fillna(1)
styles["facecolor"] = styles["facecolor"].fillna(self._facecolor)
styles["edgecolor"] = styles["edgecolor"].fillna(styles["facecolor"])
styles["linestyle"] = styles["linestyle"].fillna("solid")

Then if you go back to UpSetPlot/ directory, you can run python

>>> import local_upsetplot as up
>>> # then do everything as in the examples, it works !

So the pb is : they fixed the error, but somehow it didn't synchronized with the version that we can download ...