Cleanup: Use filesystem instead of experimental

The GCC version bump in Yocto 2.6 allows for use of std::filesystem
instead of std::experimental::filesystem.

Change-Id: Ibfd6c285bcbd6695e5cd4e3090ffa214fc861499
Signed-off-by: Brandon Wyman <bjwyman@gmail.com>
diff --git a/pmbus.hpp b/pmbus.hpp
index 22452cf..cb244fd 100644
--- a/pmbus.hpp
+++ b/pmbus.hpp
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <experimental/filesystem>
+#include <filesystem>
 #include <string>
 #include <vector>
 
@@ -9,7 +9,7 @@
 namespace pmbus
 {
 
-namespace fs = std::experimental::filesystem;
+namespace fs = std::filesystem;
 
 // The file name Linux uses to capture the STATUS_WORD from pmbus.
 constexpr auto STATUS_WORD = "status0";