Use correct dashes instead of hypens

[MaxGabriel]

LGTM. Practical Typography suggests em dashes without spaces, but notes that The El­e­ments of Ty­po­graphic Style recommends en dashes with spaces (which is what was used in this PR).

[rivalitaet]

There's a long discussion about using em dashes vs en dashes, every style guide prefers differently. I usually prefer en dashes, because they don't shine out that much. Also I didn't want to change Snoyberg's text too much – en dashes look more like hyphens.