requirements: update ansible version

The zuul_stream callback needs ansible>=2.3 for the _handle_exception method.

Change-Id: I9130aaacc036c2e67fea31efe54c4cbaf7193f50
diff --git a/requirements.txt b/requirements.txt
index 81f930e..5caa1b5 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -16,7 +16,7 @@
 apscheduler>=3.0
 PrettyTable>=0.6,<0.8
 babel>=1.0
-ansible>=2.0.0.1
+ansible>=2.3.0.0
 kazoo
 sqlalchemy
 alembic