docs: Update switcher.json for v0.19.3

Author: Conengmo

docs/_static/switcher.json

@@ -4,10 +4,14 @@
     "url": "https://python-visualization.github.io/folium/dev/"
   },
   {
-    "name": "latest (0.19.2)",
-    "version": "0.19.2",
+    "name": "latest (0.19.3)",
+    "version": "0.19.3",
     "url": "https://python-visualization.github.io/folium/latest/"
   },
+  {
+    "version": "0.19.2",
+    "url": "https://python-visualization.github.io/folium/v0.19.2/"
+  },
   {
     "version": "0.19.1",
     "url": "https://python-visualization.github.io/folium/v0.19.1/"