Update lectures/back_prop.md

Author: mmcky

lectures/back_prop.md

@@ -23,6 +23,7 @@ In addition to what's included in base Anaconda, we need to install the followin
 
 !pip install -U kaleido plotly
 !conda install -y -c plotly plotly-orca
+!plotly_get_chrome
 ```
 
 We also need to install JAX to run this lecture