Fix error when running `make` / `docker-compose up`

This fixes an error when running the mobilizon_api container (either
with `make` or `docker-compose up`): the command `mix phx.server`
was run first in the mobilizon_api container, but it
made the container restart every ~10 seconds because of missing
dependencies errors. As a result it became impossible to install
the depencies using
`docker-compose exec api sh -c "cd js && yarn install && cd ../"`,
because that would give this error:
`Error response from daemon: Container
8ff288ad74565bb0773f9b5f8fb39ab62925c16ea0ca77c5d2579cc3013a8464 is
restarting, wait until the container is running`.

This commit fixes this error by running the dependency installation
commands (and compilation and db migration) before `mix phx.server`.

Makefile

@@ -5,11 +5,6 @@ init:
 start: stop
 	@bash docker/message.sh "starting Mobilizon with docker"
 	docker-compose up -d api
-	docker-compose exec api sh -c "cd js && yarn install && cd ../"
-	docker-compose exec api mix deps.get
-	docker-compose exec api mix compile
-	docker-compose exec api mix ecto.create
-	docker-compose exec api mix ecto.migrate
 	@bash docker/message.sh "started"
 stop:
 	@bash docker/message.sh "stopping Mobilizon"

docker-compose.yml

@@ -30,7 +30,15 @@ services:
       MOBILIZON_DATABASE_USERNAME: postgres
       MOBILIZON_DATABASE_DBNAME: mobilizon_dev
       MOBILIZON_DATABASE_HOST: postgres
-    command: "mix phx.server"
+    command: >
+      sh -c "cd js &&
+      yarn install &&
+      cd ../ &&
+      mix deps.get &&
+      mix compile &&
+      mix ecto.create &&
+      mix ecto.migrate &&
+      mix phx.server"
 volumes:
   pgdata:
   .: