use filesystem instead of experimental

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

Change-Id: I62838b343ce34f85a47661f1eaaff3c7e6338bbf
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/sysfs.cpp b/sysfs.cpp
index ba07c15..e554afe 100644
--- a/sysfs.cpp
+++ b/sysfs.cpp
@@ -20,14 +20,14 @@
 #include <algorithm>
 #include <cerrno>
 #include <cstdlib>
-#include <experimental/filesystem>
+#include <filesystem>
 #include <fstream>
 #include <memory>
 #include <phosphor-logging/log.hpp>
 #include <thread>
 
 using namespace std::string_literals;
-namespace fs = std::experimental::filesystem;
+namespace fs = std::filesystem;
 
 namespace sysfs
 {