[travis] enable Redis cluster

Author: nicolas-grekas

.travis.yml

@@ -41,6 +41,7 @@ services:
     - mongodb
     - redis-server
     - rabbitmq
+    - docker
 
 before_install:
     - |
@@ -164,6 +165,11 @@ before_install:
       fi
 
 install:
+    - |
+      # start redis cluster
+      docker pull grokzen/redis-cluster:4.0.8
+      docker run -d -p 7000:7000 -p 7001:7001 -p 7002:7002 -p 7003:7003 -p 7004:7004 -p 7005:7005 --name redis-cluster grokzen/redis-cluster:4.0.8
+
     - |
       # Create local composer packages for each patched components and reference them in composer.json files when cross-testing components
       if [[ ! $deps ]]; then