Minor spelling issue in installation script

[meglio (Anton)]

Installing a fresh Discourse instance. It looks like some file path or domain name is missing:

[mpalmer (Matt Palmer)]

Looks like it was broken by Update samples (#387) · discourse/discourse_docker@f5cf127 · GitHub. PR welcome!

[pfaffman (Jay Pfaffman)]

I’m on it. I’ll add it to my list.