[Etherpad] Fix booleans in environment

pica-etherpad/docker-compose.yml

@@ -31,13 +31,13 @@ services:
       traefik.port: 8080
     environment:
       DB_HOST: "etherpad-db"
-      EDIT_ONLY: true
+      EDIT_ONLY: "true"
       LOGLEVEL: "INFO"
-      MINIFY: "TRUE"
+      MINIFY: "true"
       PORT: 8080,
       THEME: "colibris"
       TITLE: "Picapad"
-      TRUE_PROXY: true
+      TRUE_PROXY: "true"
     restart: unless-stopped
     networks:
       - docker_default