use filesystem instead of experimental

Use filesystem now that it should be available instead of
experimental::filesystem.

Change-Id: Ia9b17f33ced70fe2f1f12f11d8708d15ff422bfa
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/utils_unittest.cpp b/test/utils_unittest.cpp
index b986bd8..6b89f6a 100644
--- a/test/utils_unittest.cpp
+++ b/test/utils_unittest.cpp
@@ -4,14 +4,14 @@
 #include "manager_mock.hpp"
 #include "utils.hpp"
 
-#include <experimental/filesystem>
+#include <filesystem>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include <gtest/gtest.h>
 
-namespace fs = std::experimental::filesystem;
+namespace fs = std::filesystem;
 
 namespace blobs
 {