apex: unmount flattened apex directory before installing zips

Change-Id: Idd1cadedcab94e81e30a487bd09f9173e5fe577e
diff --git a/twrpApex.hpp b/twrpApex.hpp
index edd1d5f..1c85d06 100755
--- a/twrpApex.hpp
+++ b/twrpApex.hpp
@@ -15,6 +15,7 @@
 #include <sys/sysmacros.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <android-base/properties.h>
 
 #include <ziparchive/zip_archive.h>
 #include "twcommon.h"