Improve Dockerfile (ludwig-ai#106)

- Added newlines for readability
- Added depth parameter to git clone so not the full git history is cloned
- Combined git clone and Ludwig installation into one layer

Author: philippgille

Dockerfile

@@ -1,8 +1,12 @@
 FROM tensorflow/tensorflow:latest-py3
 
-RUN apt-get install -y --no-install-recommends git
-RUN git clone https://github.com/uber/ludwig.git
-RUN cd ludwig/ && pip install -r requirements.txt && python -m spacy download en && python setup.py install
+RUN apt-get install -y --no-install-recommends \
+        git
+RUN git clone --depth=1 https://github.com/uber/ludwig.git \
+    && cd ludwig/ \
+    && pip install -r requirements.txt \
+    && python -m spacy download en \
+    && python setup.py install
 
 WORKDIR /data