Organise Dockerfile better

Dockerfile

@@ -1,25 +1,21 @@
 FROM python:3.7-slim-buster
 
 ARG ELECTRUM_VERSION=3.3.8
-
 ENV ELECTRUM_INSTALL_DIR /opt/electrum
 
-RUN apt-get update
+RUN mkdir $ELECTRUM_INSTALL_DIR
+WORKDIR $ELECTRUM_INSTALL_DIR
 
+RUN apt-get update
 RUN apt-get install -y git
 RUN git clone git://github.com/spesmilo/electrum.git $ELECTRUM_INSTALL_DIR 
-
-WORKDIR $ELECTRUM_INSTALL_DIR 
-
 RUN git checkout $ELECTRUM_VERSION
 RUN git submodule update --init
 RUN apt-get install -y libsecp256k1-0
 RUN python3 -m pip install --user . cryptography
-
 RUN ln -s $ELECTRUM_INSTALL_DIR/run_electrum /usr/bin/electrum
 
 WORKDIR /root
 
 ADD ./entrypoint.sh /entrypoint.sh
-
 ENTRYPOINT ["/entrypoint.sh"]