Install electrum into /opt/electrum

Dockerfile

@@ -2,19 +2,23 @@ FROM python:3.7-slim-buster
 
 ARG ELECTRUM_VERSION=3.3.8
 
+ENV ELECTRUM_INSTALL_DIR /opt/electrum
+
 RUN apt-get update
 
 RUN apt-get install -y git
-RUN git clone git://github.com/spesmilo/electrum.git
+RUN git clone git://github.com/spesmilo/electrum.git $ELECTRUM_INSTALL_DIR 
 
-WORKDIR electrum
+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/run_electrum /usr/bin/electrum
+RUN ln -s $ELECTRUM_INSTALL_DIR/run_electrum /usr/bin/electrum
+
+WORKDIR /root
 
 ADD ./entrypoint.sh /entrypoint.sh