Add Java runtime to CHRIS container

Dockerfile

@@ -10,6 +10,10 @@ COPY . /app
 # Install Flask
 RUN pip install --no-cache-dir -r requirements.txt
 
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends default-jre-headless && \
+    rm -rf /var/lib/apt/lists/*
+
 # Expose default port
 EXPOSE 7860