use filesystem instead of experimental

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

Change-Id: I8648ac2b279eea42c13d6b12f312a2e1e02aa152
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/sysfs/util.cpp b/sysfs/util.cpp
index aeceada..d73ec0f 100644
--- a/sysfs/util.cpp
+++ b/sysfs/util.cpp
@@ -16,7 +16,7 @@
 
 #include "sysfs/util.hpp"
 
-#include <experimental/filesystem>
+#include <filesystem>
 #include <iostream>
 #include <string>
 
@@ -31,7 +31,7 @@
  */
 
 static constexpr auto platform = "/sys/devices/platform/";
-namespace fs = std::experimental::filesystem;
+namespace fs = std::filesystem;
 
 std::string FixupPath(std::string original)
 {