Increment CMake Version Number

[Kerilk]

Should the version number here be updated:

OpenCL-Headers/CMakeLists.txt

Lines 3 to 7 in 59ac4dc

	project(OpenCLHeaders
	VERSION 2.2
	LANGUAGES C # Ideally should be NONE, but GNUInstallDirs detects platform arch using try_compile
	# https://stackoverflow.com/questions/43379311/why-does-project-affect-cmakes-opinion-on-cmake-sizeof-void-p
	)

[bashbaug]

Gut feeling: yes, it should, although it looks like it's currently only being used for the CMake package so it (currently) may not matter much in practice.

If we updated the version number what would we update it to? Obvious candidates are either 3.0.X, since the headers support up to OpenCL 3.0, or a date-based versioning to match our tags/releases.