shrink Travis usage

There is no point running builds, tests, lints on Travis, since we
already do that on Circle.

The only thing we aren't doing (and can't do) on Circle is doc
publishing, so now Travis does just that.

(cherry picked from commit 1038cbd1a3)

.travis.yml

@@ -1,28 +1,12 @@
 language: go
 sudo: false
-go:
-  - 1.4
 
 env:
   - PATH="${PATH}:${HOME}/.local/bin"
 
-addons:
-  apt:
-    packages:
-    - libpcap-dev
-
 install:
-  - go clean -i net
-  - go install -tags netgo std
-  - go get github.com/golang/lint/golint
   - pip install --user --upgrade gsutil
   - bin/setup-ci-secrets $encrypted_5ba036e89377_key $encrypted_5ba036e89377_iv
-  - make travis
-  - go get ./...
 
 script:
-  - make tests
-
-after_success:
-  - go get github.com/mattn/goveralls
-  - test "${TRAVIS_PULL_REQUEST}" = "false" && site/build-and-publish.sh
+  - 'test "${TRAVIS_PULL_REQUEST}" = "false" && site/build-and-publish.sh || true'