Fixing docker-compose build process (#471)

Currently the command `docker-compose build` throws an error for building the database because it uses an old pip version.

This PR updates pip right before it is called. Anyways this should just be a temporary fix because the image uses Python 2.7 wich out of support since Jan 2020

db/Dockerfile

@@ -15,6 +15,7 @@ RUN apk add --no-cache \
       py-cryptography \
       pv \
       libressl-dev \
+    && pip install --upgrade pip \
     && pip --no-cache-dir install -c pip-constraints.txt 'wal-e<1.0.0' envdir \
     && rm -rf /var/cache/apk/* /tmp/* /var/tmp/*