Fix dash-to-triple-hyphen replacement in generateSlug function.

If you use a [common unicode dash](https://en.wikipedia.org/wiki/Dash#Common_dashes) in your post title, your slug/url will contain three hyphens. This looks rather strange. This commit replaces those with one hyphen instead. Sometimes those dashes are used without spaces between words. Replacing them with '' would result in joining two words in the slug.

Example:
> *For ages 3–5*
> *A flock of sparrows—some of them juveniles—alighted and *sang.

Altered integration test accordingly.
Alter unit test for hyphens, dashes and spaces.