Fix include paths.

json/json_reader.cpp

@@ -1,5 +1,5 @@
-#include <json/reader.h>
-#include <json/value.h>
+#include "reader.h"
+#include "value.h"
 #include <utility>
 #include <cstdio>
 #include <cassert>

json/json_value.cpp

@@ -1,6 +1,6 @@
 #include <iostream>
-#include <json/value.h>
-#include <json/writer.h>
+#include "value.h"
+#include "writer.h"
 #include <utility>
 #include <stdexcept>
 #include <cstring>

json/json_writer.cpp

@@ -1,4 +1,4 @@
-#include <json/writer.h>
+#include "writer.h"
 #include <utility>
 #include <assert.h>
 #include <stdio.h>