update .append method for dataframes

[jGaboardi]

Description / Summary

Replace old .append() method (that's causes the warning below) with pandas.concat([df1, df2]).

momepy/preprocessing.py:273: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.

momepy/momepy/preprocessing.py

Lines 275 to 279 in 0ae6d95

	return df.append(
	gpd.GeoDataFrame({df.geometry.name: final}, geometry=df.geometry.name),
	ignore_index=True,
	)
	return df.append(final, ignore_index=True)

Probably occurs in more places within momepy than only in preprocessing.

xref #382

Value / benefit

Need to keep up with current pandas.

Implementation details

No response

Tasks to complete

No response