Ragel version detection in Rakefile is broken

Version 5.7 is lower than 5.18, the Rakefile fails to detect that. Patch
attached.

Andreas S. wrote:

Version 5.7 is lower than 5.18, the Rakefile fails to detect that. Patch
attached.

Ok, this introduces another bug (6.1 < 5.18); who would have thought
something trivial like this could be implemented wrong twice?

(@ragel_v[0] == 5 && @ragel_v[1] >= 18) || @ragel_v[0] > 5