Update api version in responses

ec2stack/templates/response.xml

diff --git a/ec2stack/templates/response.xml b/ec2stack/templates/response.xml
index c0645ef..ea170ca 100644
--- a/ec2stack/templates/response.xml
+++ b/ec2stack/templates/response.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<{{response_type}}{% if not error %} xmlns="http://ec2.amazonaws.com/doc/2014-02-01/"{%endif%}>
+<{{response_type}}{% if not error %} xmlns="http://ec2.amazonaws.com/doc/2014-05-01/"{%endif%}>
     {% block response_content %}{% endblock %}
     {% if request_id %}
     <RequestId>{{request_id}}</RequestId>