get new altair in dockerfile

Author: trevorcampbell

Dockerfile

@@ -19,6 +19,9 @@ RUN pip install referencing
 RUN pip install jupyter-book
 RUN pip install numpy jinja2 altair_data_server vl-convert-python click ibis-framework ghp-import jupytext nodejs
 
+# Update altair to >= 5.1.1 get a png rendering in PDF build
+RUN pip install --upgrade altair
+
 # forces scikit-learn to grab latest to avoid bug in 1.3.0 related to checking for c-contiguity breaking figures in classification 2. See https://github.com/scikit-learn/scikit-learn/pull/26772
 # TODO: remove this once scikit-learn 1.4.x or beyond releases and is incorporated into jupyter/scipy-notebook
 RUN pip install -U git+https://github.com/scikit-learn/scikit-learn.git@main