(check_xml_dependencies): sheldon fails when xml object does not have a type attribute

Summary

type attribute is optional when object is a ref, but sheldon fails when trying to find the namespace.

Sheldon fails with the following line :

   <object uid="${selection}" src="ref" />

Steps to reproduce

Launch sheldon on ioActivity/plugin.xml

What is the current bug behavior?

* [Sheldon] 1 file(s) checked.
*** [ERROR] Dependency missing in Bundles/activity/ioActivity/rc/plugin.xml :
'type'
 ***

What is the expected correct behavior?

No fail