[WM] upgrade Immutant to 1.1.1

I was trying to see if this would fix an issue I was having running this
locally, but I don't think they were related. Anyway, good to stay
current regardless.

I also improved how we interpolate the IMMUTANT_VERSION variable.
Merge pull request #4 from turbovote/upgrade-immutant-to-1.1.1

[WM] upgrade Immutant to 1.1.1