Gallery example "Color points by categories": Update "color" to "fill…

…" in introduction text (#3340)

examples/gallery/symbols/points_categorical.py

@@ -6,8 +6,8 @@
 color-coded by categories. In the example below, we show how the
 `Palmer Penguins dataset <https://github.com/allisonhorst/palmerpenguins>`__
 can be visualized. Here, we can pass the individual categories included in
-the "species" column directly to the ``color`` parameter via
-``color=df.species.cat.codes.astype(int)``. Additionally, we have to set
+the "species" column directly to the ``fill`` parameter via
+``fill=df.species.cat.codes.astype(int)``. Additionally, we have to set
 ``cmap=True``. A desired colormap can be selected via the :func:`pygmt.makecpt`
 function.
 """