Bump 2.x version to fix CMake compilation on /usr-merged distros

[kouta-kun]

Hi! Lately, I've been having issues building projects that use SDL_net on distros that have gone through the /usr merge (Debian, Arch Linux, probably some more). As I can see in the repository, this has already been fixed:

SDL_net/sdl2_net-config.cmake.in

Line 11 in b29ffae

get_filename_component(CMAKE_CURRENT_LIST_DIR ${CMAKE_CURRENT_LIST_DIR} REALPATH)

But a new release + version bump has not been created since then, and some distros such as Arch Linux will not ship these kinds of changes as patches. Would it be possible to generate a 2.3.0 or 2.2.1 version bump so that this fix can be propagated into these distros?