Set host properly on nginx dev container

docker/nginx/entrypoint.sh

 #!/bin/bash -eux
-
+FIRST_HOST=$(echo ${DJANGO_ALLOWED_HOSTS} | cut -d, -f1)
 echo "Copying template file..."
 cp /etc/nginx/funkwhale_proxy.conf{.template,}
-sed -i "s/X-Forwarded-Host \$host:\$server_port/X-Forwarded-Host localhost:${WEBPACK_DEVSERVER_PORT}/" /etc/nginx/funkwhale_proxy.conf
+sed -i "s/X-Forwarded-Host \$host:\$server_port/X-Forwarded-Host ${FIRST_HOST}:${WEBPACK_DEVSERVER_PORT}/" /etc/nginx/funkwhale_proxy.conf
+sed -i "s/proxy_set_header Host \$host/proxy_set_header Host ${FIRST_HOST}/" /etc/nginx/funkwhale_proxy.conf
 sed -i "s/proxy_set_header X-Forwarded-Port \$server_port/proxy_set_header X-Forwarded-Port ${WEBPACK_DEVSERVER_PORT}/" /etc/nginx/funkwhale_proxy.conf
 
 cat /etc/nginx/funkwhale_proxy.conf