Re-based to Slim, reduced NTLK corpus dependencies

Image now has a much smaller footprint of ca 300 MB rather than 9 GB

posting/Dockerfile

@@ -1,7 +1,7 @@
 FROM python:slim
 COPY . /usr/src/app
 WORKDIR /usr/src/app
-RUN pip install --upgrade pip
-RUN pip install -r requirements.txt
-RUN python -m nltk.downloader all
+RUN pip install --upgrade pip && pip install -r requirements.txt && \
+    apt-get autoremove -y
+RUN python -m nltk.downloader wordnet
 CMD python3 -u ./script.py