Replace include guards with #pragma once

Change-Id: I16adc78d397e3239440206e8e70ebbd5e0963adb
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/argument.hpp b/argument.hpp
index 3cb7e68..ed2399a 100644
--- a/argument.hpp
+++ b/argument.hpp
@@ -1,5 +1,5 @@
-#ifndef __ARGUMENT_H
-#define __ARGUMENT_H
+#pragma once
+
 #include <getopt.h>
 #include <map>
 #include <string>
@@ -25,6 +25,4 @@
         ArgumentParser() {};
 };
 
-#endif
-
 // vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4