rq need redis-server

.travis.yml

@@ -7,6 +7,7 @@ python:
 
 services:
   - docker
+  - redis-server
 
 before_install:
   - docker pull mailhog/mailhog

README.md

@@ -19,6 +19,7 @@ on Debian Stretch (9) with sudo:
     sudo apt update
     sudo apt install git
     sudo apt install python3 python3-venv python3-dev python3-pip
+    sudo apt install redis-server
 
 ### Get the source ###