watch: IWYU

Change-Id: I378a514981660cf62e61bfbb2112155ee657320d
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/watch.hpp b/watch.hpp
index bf16742..d98c322 100644
--- a/watch.hpp
+++ b/watch.hpp
@@ -1,9 +1,10 @@
 #pragma once
-#include "watch.hpp"
-
+#include <functional>
 #include <memory>
 #include <sdeventplus/source/event.hpp>
 #include <sdeventplus/source/io.hpp>
+#include <string>
+
 namespace phosphor
 {
 namespace certs