Grouped RUN in Dockerfile (progress for #5)

Dockerfile

@@ -1,18 +1,20 @@
 FROM ruby
+
+# Copy the requirements.txt first, as it'll be used for pip install
+COPY requirements.txt .
+
 # Install python3 and pip for the API, and ruby for anystyle-cli
 RUN apt-get update -y && apt-get upgrade -y && \
-    apt-get install -y python3 python3-pip
-RUN gem install anystyle-cli
+    apt-get install -y python3 python3-pip && \
+    gem install anystyle-cli && \
+    pip3 install -r requirements.txt
 
-COPY requirements.txt .
 COPY app/ /app
 COPY model/ /app/model
 COPY grobid_client/ /app/grobid_client
 # In Docker, use a different JSON file (hostname then gets changed to Docker container name)
 COPY docker-config.json /app/grobid_client/config.json
 
-RUN pip3 install -r requirements.txt
-
 # Flask is currently always configured for development settings
 ENV FLASK_APP=a.py
 ENV FLASK_ENV=development