Update apache:couchdb Docker image to 2.3 (#267)

diff --git a/docker-compose/docker-compose-lean.yml b/docker-compose/docker-compose-lean.yml
index addb478..575d4be 100644
--- a/docker-compose/docker-compose-lean.yml
+++ b/docker-compose/docker-compose-lean.yml
@@ -3,7 +3,7 @@
 version: '3'
 services:
   db:
-    image: apache/couchdb:2.1
+    image: apache/couchdb:2.3
     ports:
       - "5984:5984"
     environment: