Better dark age Goths change: Make barracks provide 10 or 15 pop space.

The current change to goths (35% cheaper militia in dark age) is too strong. This buff would incentivise barracks construction and implicitly make them cheaper without altering their upfront cost and so prevent rushing.

Thoughts?

I was messing around with other balance alternatives (e.g. -100 wood on first barracks) but they too make rushing too easy.