Bump CMake requirements to Debian bullseye

CMake versions lower than 3.5 will not be supported by CMake anymore, so a bump is needed.
Debian "old-old-stable"'s (Bullseye) version has been chosen

source/CMakeLists.txt

@@ -1,7 +1,7 @@
 #######################################
 # Required CMake version              #
 #######################################
-cmake_minimum_required( VERSION 3.3 )
+cmake_minimum_required( VERSION 3.18 )
 
 #######################################
 # Project name                        #