Fix error in ZLIB detection
I'm getting this message on screen when CMake configures the project:
The package name passed to `find_package_handle_standard_args` ;(ZLIB) does
not match the name of the calling package ;(zlib). This can lead to
problems in calling ;code that expects `find_package` result variables
(e.g., `_FOUND`) ;to follow a certain pattern.
Call Stack (most recent call first):
/home/carlo/inst_cmake/share/cmake-3.17.3/Modules/FindPackageHandleStandardArgs.cmake:272 (message)
cmake/Findzlib.cmake:39 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
src/CMakeLists.txt:13 (find_package)
This happens because the target must be "ZLIB", with capital letters, and not "zlib":
https://cmake.org/cmake/help/git-master/module/FindZLIB.html