Update mkdocs-material, better dark mode for code blocks

Signed-off-by: Stefan Scherer <stefan.scherer@docker.com>

Dockerfile

@@ -1,6 +1,7 @@
 # Install the base requirements for the app.
 # This stage is to support development.
 FROM python:alpine AS base
+RUN apk add build-base
 WORKDIR /app
 COPY requirements.txt .
 RUN pip install -r requirements.txt