Change #include style

Header files are now always included with their path from the
project's root directory rather than the path relative to
the includer.

Change-Id: If39b8510eef8da00baf5fe88337c45dbdf8c766e
Refs: #3084
diff --git a/tests/unit/util/string-helper.t.cpp b/tests/unit/util/string-helper.t.cpp
index 0456a35..ae89ba7 100644
--- a/tests/unit/util/string-helper.t.cpp
+++ b/tests/unit/util/string-helper.t.cpp
@@ -19,13 +19,14 @@
  * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
  */
 
-#include "util/string-helper.hpp"
-#include "encoding/buffer.hpp"
+#include "ndn-cxx/util/string-helper.hpp"
+#include "ndn-cxx/encoding/buffer.hpp"
 
-#include "boost-test.hpp"
+#include "tests/boost-test.hpp"
 
 #include <cctype>
 #include <cstring>
+#include <boost/test/output_test_stream.hpp>
 
 namespace ndn {
 namespace util {