Change minimum required CMake version to 3.20

This is the same requirement as for building WPE WebKit itself.

Author: aperezdc

CMakeLists.txt

@@ -1,5 +1,4 @@
-cmake_minimum_required(VERSION 3.0)
-cmake_policy(VERSION 3.0)
+cmake_minimum_required(VERSION 3.20)
 
 set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 include(VersioningUtils)