normalizeCiphertext corrected grouping size

The previous spec is inconsistent in how it tests 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. Edited so `normalizeCiphertext` now follows the same pattern as `plaintextSegments,` which should generate less confusion for people attempting to interpret the spec.

As a corollary, updated the `example.js` to match and pass spec. Also, replaced double quotes with single quotes.