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
go:
- tip
os:
- linux
- osx
before_install:
- go get github.com/mattn/goveralls
- go get golang.org/x/tools/cmd/cover
script:
- $HOME/gopath/bin/goveralls -repotoken 3gHdORO5k5ziZcWMBxnd9LrMZaJs8m9x5