FindRuby: fix usage of RUBY_VERSION_MAJOR (#12172)

Alex

Modules/FindRuby.cmake

@@ -60,7 +60,7 @@ ENDIF("${Ruby_FIND_VERSION_SHORT_NODOT}" VERSION_LESS "19")
 FIND_PROGRAM(RUBY_EXECUTABLE NAMES ${_RUBY_POSSIBLE_EXECUTABLE_NAMES})
 
 
-IF(RUBY_EXECUTABLE  AND NOT  RUBY_MAJOR_VERSION)
+IF(RUBY_EXECUTABLE  AND NOT  RUBY_VERSION_MAJOR)
   # query the ruby version
    EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['MAJOR']"
       OUTPUT_VARIABLE RUBY_VERSION_MAJOR)
@@ -135,7 +135,7 @@ IF(RUBY_EXECUTABLE  AND NOT  RUBY_MAJOR_VERSION)
      RUBY_VERSION_MINOR
      RUBY_VERSION_PATCH
      )
-ENDIF(RUBY_EXECUTABLE  AND NOT  RUBY_MAJOR_VERSION)
+ENDIF(RUBY_EXECUTABLE  AND NOT  RUBY_VERSION_MAJOR)
 
 # In case RUBY_EXECUTABLE could not be executed (e.g. cross compiling)
 # try to detect which version we found. This is not too good.