normalizeCiphertext corrected grouping size

The previous spec was inconsistent in how it tested output strings. plaintextSegments tested for output based on square size, e.g. a 26-character input resulted in output of groups of 6 with a group of 2 left over. normalizeCiphertext however always expected groups of 5. Corrected so normalizeCiphertext follows the same pattern as plaintextSegments.

Also updated the example.js to match.