[config, 1.9.3] Workaround OpenStruct not having []= in 1.9.3
[config, 1.9.3] Workaround OpenStruct not having []= in 1.9.3

OpenStruct gets []= at some point, but it doesn't have it in 1.9.3.

I develop in 2.1.0, and so I didn't notice this. Travis helped me out
here.

jedcn/reveal-ck,jedcn/reveal-ck,jedcn/reveal-ck