Fix that CMake version check again

tests/CMakeLists.txt

@@ -1,6 +1,6 @@
-IF(CMAKE_MAJOR_VERSION LESS 2 AND
-   CMAKE_MINOR_VERSION LESS 8 AND
-   CMAKE_PATCH_VERSION LESS 8)
+IF(NOT (CMAKE_MAJOR_VERSION GREATER 2 OR
+   CMAKE_MINOR_VERSION GREATER 8 OR
+   CMAKE_PATCH_VERSION GREATER 7))
 	MESSAGE("-- Unit tests are only available in CMake >=2.8.8. You have ${CMAKE_VERSION}")
 	RETURN()
 ENDIF()