Just tried it on 1.2, and it doesn't load the mod. It looks like 1.1.3 is the version you need.
I don't use Steam for KSP (WHAT?!), so I'm not sure how to get 1.1.3 if that's the route you've taken. Otherwise, you can download it from the KSP site: https://kerbalspaceprogram.com/en/
Click BUY NOW in the top-right of the screen.
Enter your account credentials (assuming you've already purchased it via this method).
Click My Account to the right of your name.
Click the Download button on the line item of your original purchase.
Scroll down to the Kerbal Space Program 1.1.3 section, and select the OS and installation type you want.
One of the guys above me laid out how to do it through Steam, or you can buy it through the KSP site. I've actually done both since I was having trouble with Steam on Ubuntu a while back. It's a game worth paying for twice.
