GIMME_OS=windows not working

[Jille]

https://travis-ci.org/Jille/rufs/jobs/152098169 shows:

Setting environment variables from .travis.yml
$ export GIMME_OS=windows
$ export GIMME_ARCH=amd64
14.25s$ GIMME_OUTPUT=$(gimme 1.6) && eval "$GIMME_OUTPUT"
error: Missing bootstrap installation
error: Unable to compile go from git clone
error: Missing bootstrap installation
error: Unable to compile go from git clone
I don't have any idea what to do with '1.6'.
  (using type 'auto')
The command "GIMME_OUTPUT=$(gimme 1.6) && eval "$GIMME_OUTPUT"" failed and exited with 1 during .
Your build has been stopped.

My config file is
https://github.com/Jille/rufs/blob/travis_windows/.travis.yml

language: go

go:
- 1.6

env:
- GIMME_OS=linux GIMME_ARCH=386
- GIMME_OS=linux GIMME_ARCH=amd64
- GIMME_OS=windows GIMME_ARCH=386
- GIMME_OS=windows GIMME_ARCH=amd64

install:
- go get ./...

script:
- "[ `gofmt -l *.go | wc -l` = 0 ]"
- go build