Installing with Racket 8.5

[nano-o]

Hello,
I tried to install gamble using Racket 8.5 with raco pkg install git://github.com/rmculpepper/gamble and it produced the following error:

/home/nano/.racket/8.5/pkgs/gamble/gamble/private/instrument.rkt:341:33: pred: use does not match pattern: (pred y a)
  in: (pred obs-v)
  compilation context...:
   /home/nano/.racket/8.5/pkgs/gamble/gamble/tests/observe.rkt
  location...:
   /home/nano/.racket/8.5/pkgs/gamble/gamble/private/instrument.rkt:341:33
  context...:
   /home/nano/racket/collects/racket/private/stxparam.rkt:61:2
   [repeats 2 more times]
   /home/nano/racket/collects/compiler/private/cm-minimal.rkt:685:0: compile-zo*
   /home/nano/racket/collects/compiler/private/cm-minimal.rkt:451:15
   /home/nano/racket/collects/compiler/private/cm-minimal.rkt:440:12: build
   /home/nano/racket/collects/compiler/private/cm-minimal.rkt:411:0: maybe-compile-zo
   /home/nano/racket/collects/compiler/private/cm-minimal.rkt:209:0: compile-root
   /home/nano/racket/collects/compiler/private/cm-minimal.rkt:105:4
   /home/nano/racket/collects/setup/parallel-build.rkt:332:9
   /home/nano/racket/collects/setup/parallel-do.rkt:455:25
   /home/nano/racket/collects/setup/parallel-do.rkt:441:20: loop