phosphor-settingsd: use c++17

Update configure.ac to choose the c++17 standard

Change-Id: I5aa098f4d573ce14f8d5ee5c74f1b85fd10d1bb6
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
diff --git a/configure.ac b/configure.ac
index ec6df59..ecfda4e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -21,7 +21,7 @@
 
 LT_INIT
 
-AX_CXX_COMPILE_STDCXX_14([noext])
+AX_CXX_COMPILE_STDCXX_17([noext])
 AX_APPEND_COMPILE_FLAGS([-Wall -Werror], [CXXFLAGS])
 
 AC_ARG_VAR(SETTINGS_BUSNAME, [The Dbus busname to own])