Fix redeclaration warning on opensolaris

src/GZipFile.h

@@ -36,10 +36,10 @@
 #ifndef D_GZIP_FILE_H
 #define D_GZIP_FILE_H
 
-#include <zlib.h>
-
 #include "IOFile.h"
 
+#include <zlib.h>
+
 namespace aria2 {
 
 class GZipFile: public IOFile {