Tooltip for vector tile data-join should only show matching property, not all props from vector tile

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Some of the examples [here](https://nbviewer.jupyter.org/github/mapbox/mapboxgl-jupyter/blob/master/examples/notebooks/choropleth-viz-example.ipynb) have tooltips with multiple items in them. However when I create my visualization I only get the "vector_join_property" and "color_property" keys and values in the tooltip but not the others. In this case "year":2014 is missing. Any idea why?

```
data = [{'pfafid_30spfaf06':233036, "year":2014,"value":42}]

viz = mapboxgl.viz.ChoroplethViz(data = data,
vector_url='mapbox://rutgerhofste.hybas06_v04_V04',
vector_layer_name='hybas06_v04', # Warning should match name on mapbox.
vector_join_property='pfaf_id',
data_join_property= "pfafid_30spfaf06",
color_property="value",
color_function_type='match',
color_stops= color_stops_category,
line_color = 'rgba(0,0,0,0.05)',
line_width = 0.5,
opacity=0.7,
center=(5, 52),
zoom=4,
below_layer='waterway-label'
)

```


and

Start by reproducing the tooltip behavior in the linked choropleth-viz-example.ipynb using the supplied data and ChoroplethViz configuration. Inspect how the vector tile properties are selected for the tooltip, clarify whether year should appear alongside the join and color properties, and verify the resulting tooltip against the reported examples.

Written by the indexing model from the issue text.