Move filesystem from experimental namespace

Splice it into standard for gcc8

Change-Id: I584206dd737c9d90cf93bfa8541980fdd8f6d39b
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/include/webassets.hpp b/include/webassets.hpp
index 81bed50..9bd40db 100644
--- a/include/webassets.hpp
+++ b/include/webassets.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include "filesystem.hpp"
+
 #include <crow/app.h>
 #include <crow/http_request.h>
 #include <crow/http_response.h>
@@ -7,7 +9,6 @@
 
 #include <boost/algorithm/string/replace.hpp>
 #include <boost/container/flat_set.hpp>
-#include <experimental/filesystem>
 #include <fstream>
 #include <string>
 
@@ -16,7 +17,7 @@
 namespace webassets
 {
 
-namespace filesystem = std::experimental::filesystem;
+namespace filesystem = std::filesystem;
 
 struct CmpStr
 {