tools/power turbostat: update version number

Today is 19.08.31, at least in some parts of the world.
Signed-off-by: Len Brown <len.brown@intel.com>

tools/power/x86/turbostat/turbostat.c

@@ -5306,7 +5306,7 @@ int get_and_dump_counters(void)
 }
 
 void print_version() {
-	fprintf(outf, "turbostat version 19.03.20"
+	fprintf(outf, "turbostat version 19.08.31"
 		" - Len Brown <lenb@kernel.org>\n");
 }