short_description is just basestring (#35)

As of ansible/ansible 883f451158
'short_description' value is expected to only be a string.

This should catch issues like
https://github.com/ansible/ansible/issues/17634

ansible_testing/schema.py

@@ -32,7 +32,7 @@ option_schema = Schema(
 doc_schema = Schema(
     {
         Required('module'): basestring,
-        'short_description': Any(basestring, [basestring]),
+        'short_description': basestring,
         'description': Any(basestring, [basestring]),
         'version_added': Any(basestring, float),
         'author': Any(None, basestring, [basestring]),