Fix supervisor install fails with easy_install

`easy_install` does not support https, which has been made mandatory for
pip packages. `pip` supports it natively.

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Removed
 ### Fixed
+- [nginx] `easy_install supervisor` fails
 
 
 ## [1.4.0] - 2021-01

dockerfiles/nginx/Dockerfile

@@ -90,8 +90,8 @@ RUN chown -R www-data:www-data /opt/nginx/html/secure
 RUN chmod a+x /opt/nginx/html/secure/shib_test.pl
 
 # install supervisor
-RUN apt-get update && apt-get install python-setuptools
-RUN easy_install supervisor
+RUN apt-get update && apt-get install python-pip
+RUN pip install supervisor
 COPY supervisord.conf /etc/
 RUN mkdir -p /var/log/supervisor
 # create dirs for php-fpm socket/pid and log files