Don't emit a trailng newline in base64-encoded data like 'image/png' (#13941)...
Don't emit a trailng newline in base64-encoded data like 'image/png' (#13941)
This addresses the issue highlighted in
https://github.com/jupyter/jupyter_client/issues/930
Since, unlike the latest Jupyter, IPython aims to support python<3.6,
I'm using an approach that won't break this compatibility.