added js dependencies

Dockerfile

@@ -11,13 +11,15 @@ RUN export DEBIAN_FRONTEND=noninteractive && \
         python3-pip \
         python3-virtualenv \
         python3-dev \
-        python3-setuptools
+        python3-setuptools \
+        npm
 
 # Install pelican and dependencies
 COPY files/start.sh /start.sh
 COPY files/requirements.txt requirements.txt
 RUN pip3 install wheel
 RUN pip3 install -r requirements.txt
+RUN npm install cssnano postcss postcss-cssnext postcss-import postcss-preset-env
 
 # Cleanup
 RUN apt-get autoremove --yes $build_dependencies && apt-get autoremove --yes && \