Add .travis.yml

Initially just building the linuxkit tool itself on linux, darwin and windows
with Go 1.9 and master.

Signed-off-by: Ian Campbell <ijc@docker.com>

.travis.yml

@@ -0,0 +1,22 @@
+language: go
+
+go:
+  - 1.9.x
+  - master
+
+env:
+  - TRAVIS_GOOS=linux
+  - TRAVIS_GOOS=darwin
+  - TRAVIS_GOOS=windows
+
+script:
+# We want native versions of the tools.
+  - go get -u github.com/golang/lint/golint
+  - go get -u github.com/gordonklaus/ineffassign
+  - export GOOS=$TRAVIS_GOOS
+# FIXME: For non-linux GOOS, without running `go build -i`, vet fails with `vet: import failed: can't find import: fmt`...
+# Note that `go build -i` requires write permission to GOROOT. (So it is not called in Makefile)
+  - go build -i github.com/linuxkit/linuxkit/src/cmd/linuxkit
+  - make local-check
+  - make local-build
+  - if [ "$GOOS" = "linux" ]; then make local-test ; fi