fixed typo in readme (#677)

Author: wti806

firebaseuihandler/README.md

@@ -99,7 +99,7 @@ const configs = {
       },
       // The callback to trigger when the selection tenant page
       // or enter email for tenant matching page is hidden.
-      selectTenantUihidden: () => {
+      selectTenantUiHidden: () => {
         // Hide title and additional display info.
       },
       // The callback to trigger when the sign-in page