For a long time this is the first time dmd2 trunk compiles vibe.d but ....

[Dicebot via Digitalmars-d]

tl; dr: try 0.7.21-rc.4 instead of 0.7.20

I don't know what exactly got broken in vibe.d 0.7.20 by last DMD 
releases but Sonke has mentioned it is too much of an effort to 
fix and relase 0.7.20.1