Typo in DOS Header Schema

[stkyle]

https://github.com/CybOXProject/schemas/blob/master/objects/Win_Executable_File_Object.xsd#L612

The DOS Header overlay number in the schema reads e_ovro

It should read e_ovno

Reference: http://www.csn.ul.ie/~caolan/pub/winresdump/winresdump/doc/pefile2.html