Upgrade Synapse (0.31.0 -> 0.31.1)

roles/matrix-server/defaults/main.yml

@@ -45,7 +45,7 @@ docker_postgres_image_v9: "postgres:9.6.9-alpine"
 docker_postgres_image_v10: "postgres:10.4-alpine"
 docker_postgres_image_latest: "{{ docker_postgres_image_v10 }}"
 
-docker_matrix_image: "matrixdotorg/synapse:v0.31.0"
+docker_matrix_image: "matrixdotorg/synapse:v0.31.1"
 docker_nginx_image: "nginx:1.15.0-alpine"
 docker_riot_image: "avhost/docker-matrix-riot:v0.15.4"
 docker_s3fs_image: "xueshanf/s3fs:latest"