fix include names

cppcheck isn't smart enough to recognize these are c++ headers, not c
headers.  Considering we're already inconsistent about our naming, it's
easier to just be consistent, and move the last few files to use .hpp
instead of .h.

Tested:
Code builds, no changes.

Signed-off-by: Ed Tanous <ed@tanous.net>
Change-Id: Ic348d695f8527fa4a0ded53f433e1558c319db40
diff --git a/include/cors_preflight.hpp b/include/cors_preflight.hpp
index 6fa9c0a..0a5c3cc 100644
--- a/include/cors_preflight.hpp
+++ b/include/cors_preflight.hpp
@@ -1,8 +1,8 @@
 #pragma once
 
-#include <app.h>
-#include <http_request.h>
-#include <http_response.h>
+#include <app.hpp>
+#include <http_request.hpp>
+#include <http_response.hpp>
 
 namespace cors_preflight
 {