Fix portage QA warning from current extra-cmake-modules.

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.13)
+cmake_minimum_required(VERSION 3.16)
 cmake_policy(SET CMP0063 NEW)
 project(fcitx5-cskk VERSION 1.2.0)
 set(CMAKE_CXX_FLAGS "-Wall")