Raise Minimum Version to CMake v.2.8.4

[scooperly]

In: CTL/unittest/ctlrender/CMakeLists.txt

The WORKING_DIRECTORY parameter is a feature of cmake v.2.8.4

add_test(
    NAME ctlrender
    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
    COMMAND ./test.sh $<TARGET_FILE:ctlrender>
)

#add_dependencies(check ctlrender)