Fix iframe in docs (kedro-org#1231)

Signed-off-by: Laurens Vijnck <laurens_vijnck@mckinsey.com>

Author: datajoely

docs/source/06_nodes_and_pipelines/03_modular_pipelines.md

@@ -30,7 +30,7 @@ In this section you will learn about how to take advantage of modular pipelines,
    * ``Kedro-Viz`` is able to accelerate development by [rendering namespaced](../03_tutorial/05_visualise_pipeline.md) pipelines as collapsible 'super nodes'.
 
 <iframe
-    src="http://demo.kedro.org"
+    src="https://demo.kedro.org"
     width="850",
     height="600"
 ></iframe>