BMC Serialize: Change create_directory to create_directories

This commit changes serialize.cpp's create_directory call to
create_directories because core dumps have been observed when
the directory /var/lib/obmc does not exist.

Change-Id: I7e948644dddd26a34ae33400d220698e4b1bace6
Signed-off-by: Michael Tritz <mtritz@us.ibm.com>
diff --git a/serialize.cpp b/serialize.cpp
index da9e878..d692c0f 100644
--- a/serialize.cpp
+++ b/serialize.cpp
@@ -20,7 +20,7 @@
 
     if(!fs::is_directory(PERSIST_DIR))
     {
-        fs::create_directory(PERSIST_DIR);
+        fs::create_directories(PERSIST_DIR);
     }
     std::string path = PERSIST_DIR + versionId;