adding country lines to the choropleth (#78)

Author: laurabrenskelle

notebooks/mbon_citation_visualizations.ipynb

@@ -1405,6 +1405,7 @@
     "# Update layout to set color for missing data\n",
     "fig.update_geos(\n",
     "    showcoastlines=True, coastlinecolor=\"Gray\",\n",
+    "    showcountries=True,\n",
     "    showland=True, landcolor=\"White\",\n",
     "    showocean=True, oceancolor=\"Gray\",\n",
     "    showlakes=True, lakecolor=\"Gray\"\n",