update mcapi version

Change-Id: I061a0f1336a9fe66c984abe8f61b79a739c51cc0
diff --git a/images/magnum/Dockerfile b/images/magnum/Dockerfile
index c2cb92c..c60d80f 100644
--- a/images/magnum/Dockerfile
+++ b/images/magnum/Dockerfile
@@ -18,7 +18,7 @@
 pip3 install \
     --constraint /upper-constraints.txt \
         /src/magnum \
-        magnum-cluster-api==0.24.2
+        magnum-cluster-api==0.26.0
 EOF
 
 FROM openstack-python-runtime