phosphor-dbus-monitor: use c++17

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

Change-Id: I864d373572d413b0985eee0d6c958b6c982290ef
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
diff --git a/configure.ac b/configure.ac
index 7ec92de..7209565 100644
--- a/configure.ac
+++ b/configure.ac
@@ -28,7 +28,7 @@
     AC_MSG_ERROR(["Requires sdbus++"]))
 
 # Checks for typedefs, structures, and compiler characteristics.
-AX_CXX_COMPILE_STDCXX_14([noext])
+AX_CXX_COMPILE_STDCXX_17([noext])
 AX_APPEND_COMPILE_FLAGS([-fpic -Wall -Werror], [CXXFLAGS])
 
 # Checks for library functions.