Fix build with GStreamer 1.16
gst_clear_mini_object() macro introduced in GStreamer 1.16 references g_clear_pointer() defined in GLib 2.34. Bump GLIB_VERSION_MAX_ALLOWED accordingly to avoid FTBFS when compiling with -Werror.
gst_clear_mini_object() macro introduced in GStreamer 1.16 references g_clear_pointer() defined in GLib 2.34. Bump GLIB_VERSION_MAX_ALLOWED accordingly to avoid FTBFS when compiling with -Werror.