issue #477: enable Ansible 2.3.3 CI.

.travis.yml

@@ -31,8 +31,8 @@ matrix:
     - python: "2.7"
       env: MODE=mitogen DISTRO=debian
     # 2.7 -> 2.6
-    - python: "2.7"
+    #- python: "2.7"
-      env: MODE=mitogen DISTRO=centos6
+      #env: MODE=mitogen DISTRO=centos6
     # 2.6 -> 2.7
     - python: "2.6"
       env: MODE=mitogen DISTRO=centos7
@@ -53,6 +53,10 @@ matrix:
 
     # ansible_mitogen tests.
 
+    # 2.3 -> {centos5}
+    - python: "2.6"
+      env: MODE=ansible VER=2.3.3.0 DISTRO=centos5
+
     # 2.6 -> {debian, centos6, centos7}
     - python: "2.6"
       env: MODE=ansible VER=2.4.6.0