Use vendoring for backward compatibility The switch of the Madon library to Go modules breaks builds with Go version < 1.11 since the import path now contains "v2". This patch adds vendoring so that it can still build with those versions. Let's try to re-enable Travis builds with Go v1.8-1.11...

language: go
sudo: required
go:
  - 1.7.5
  - 1.8
  - tip
os:
  - linux
matrix:
  allow_failures:
    - go: tip
  fast_finish: true
script:
  - make check