Upgrade to postgres 10

Note that beginning with version 10, a major release is indicated by
increasing the first part of the version, e.g. 10 to 11.

So 10.1 will be a minor version. That's why we can use the docker tag
"10".

See https://www.postgresql.org/support/versioning/

README.rst

@@ -69,10 +69,10 @@ Backup & restore
 To dump the database::
 
     $ docker run --rm --link csentry_postgres:postgres --net csentry_default -e PGPASSWORD="<csentry_password>"
-      postgres:9.6 pg_dump -h postgres -U csentry csentry_db | gzip > csentry_db.dump.gz
+      postgres:10 pg_dump -h postgres -U csentry csentry_db | gzip > csentry_db.dump.gz
 
 
 To restore the database::
 
     $ gunzip -c csentry_db.dump.g | docker run --rm --link csentry_postgres:postgres --net csentry_default
-      -e PGPASSWORD="<csentry_password>" -i postgres:9.6 psql -h postgres -U csentry csentry_db
+      -e PGPASSWORD="<csentry_password>" -i postgres:10 psql -h postgres -U csentry csentry_db

docker-compose.yml

@@ -7,7 +7,7 @@ services:
     depends_on:
       - postgres
   postgres:
-    image: postgres:9.6
+    image: postgres:10
     container_name: csentry_postgres
     expose:
       - "5432"