Fix JemallocNodumpAllocator when compiled without folly-config.h

Summary: HHVM compiles without `folly-config.h`, so this was preventing us from updating to the newest version of Folly.

Reviewed By: yfeldblum

Differential Revision: D4456890

fbshipit-source-id: ed118ff0cf7f254a5f99be68f171d1b34ebf5c5c

folly/experimental/JemallocNodumpAllocator.h

@@ -18,7 +18,7 @@
 
 #pragma once
 
-#include <folly/folly-config.h>
+#include <folly/portability/Config.h>
 
 #ifdef FOLLY_HAVE_LIBJEMALLOC