Fixes smart_migrate for a TypeError bug

Bug is: TypeError can't convert Rex::RuntimeError into String

[SeeRM: rapid7#7984]

Author: wchen-r7

modules/post/windows/manage/smart_migrate.rb

@@ -61,7 +61,7 @@ def attempt_migration(target_pid)
 			return true
 		rescue ::Exception => e
 			print_error("Could not migrate in to process.")
-			print_error(e)
+			print_error(e.to_s)
 			return false
 		end
 	end