Cell metadata doesn't work with jupytext

This is what jupytext thinks about our initialization cells

diff --git a/src/1_einstein_model.md b/src/1_einstein_model.md
index 1bf8b10..131b72b 100644
--- a/src/1_einstein_model.md
+++ b/src/1_einstein_model.md
@@ -1,18 +1,19 @@
 ---
 jupyter:
   jupytext:
+    cell_metadata_json: true
     text_representation:
       extension: .md
       format_name: markdown
-      format_version: '1.0'
-      jupytext_version: 1.0.2
+      format_version: '1.2'
+      jupytext_version: 1.3.3
   kernelspec:
     display_name: Python 3
     language: python
     name: python3
 ---
 
-```{python initialize=true}
+<!-- #raw {"incorrectly_encoded_metadata": "{python initialize=true}"} -->
 import pandas
 
 from matplotlib import pyplot
@@ -28,7 +29,7 @@ from common import draw_classic_axes, configure_plotting
 configure_plotting()
 
 py.init_notebook_mode(connected=True)
-```
+<!-- #endraw -->