Modify primer to utilise file_contents macro.

Author: Matthew Hall

modules/exploits/windows/fileformat/ms13_071_theme.rb

@@ -67,7 +67,7 @@ def initialize(info={})
 
   def exploit
     print_status("Creating '#{datastore['FILENAME']}' file ...")
-    self.exe_contents = generate_payload_exe
+    self.file_contents = generate_payload_exe
     print_status("Malicious SCR available on #{unc}...")
     # Default Windows XP / 2003 theme modified
     theme = <<-EOF