Replace all uses of NULL with nullptr

This was an automatic change made by clang-tidy.  It moves all uses of
NULL to nullptr, which are equivalent, but nullptr is prefered.

Tested:  Code compiles.

Signed-off-by: Ed Tanous <ed.tanous@intel.com>
Change-Id: I9526599b222693c9723a69934b599c7a5b5d1fbf
diff --git a/http/http_server.h b/http/http_server.h
index 82ba9d0..df42214 100644
--- a/http/http_server.h
+++ b/http/http_server.h
@@ -95,7 +95,7 @@
 
     void updateDateStr()
     {
-        time_t lastTimeT = time(0);
+        time_t lastTimeT = time(nullptr);
         tm myTm{};
 
         gmtime_r(&lastTimeT, &myTm);