issue #603: Revert "ci: update to Ansible 2.8.3"

This reverts commit 558ebfa914.

.travis.yml

@@ -36,25 +36,25 @@ matrix:
 
   include:
     # Debops tests.
-    # 2.8.3; 3.6 -> 2.7
+    # 2.8.0; 3.6 -> 2.7
     - python: "3.6"
-      env: MODE=debops_common VER=2.8.3
+      env: MODE=debops_common VER=2.8.0
     # 2.4.6.0; 2.7 -> 2.7
     - python: "2.7"
       env: MODE=debops_common VER=2.4.6.0
 
     # Sanity check against vanilla Ansible. One job suffices.
     - python: "2.7"
-      env: MODE=ansible VER=2.8.3 DISTROS=debian STRATEGY=linear
+      env: MODE=ansible VER=2.8.0 DISTROS=debian STRATEGY=linear
 
     # ansible_mitogen tests.
 
-    # 2.8.3 -> {debian, centos6, centos7}
+    # 2.8.0 -> {debian, centos6, centos7}
     - python: "3.6"
-      env: MODE=ansible VER=2.8.3
+      env: MODE=ansible VER=2.8.0
-    # 2.8.3 -> {debian, centos6, centos7}
+    # 2.8.0 -> {debian, centos6, centos7}
     - python: "2.7"
-      env: MODE=ansible VER=2.8.3
+      env: MODE=ansible VER=2.8.0
 
     # 2.4.6.0 -> {debian, centos6, centos7}
     - python: "3.6"