Heisenbug with a not fetched dependency in Travis

[dpordomingo]

Reported by @bzz via Slack:

For some reason, CAT build on master is failing https://travis-ci.org/src-d/code-annotation

package github.com/golang/lint/golint
imports golang.org/x/lint: unrecognized import path "golang.org/x/lint" (https fetch: Get https://golang.org/x/lint?go-get=1: net/http: TLS handshake timeout

The build was restarted and it succeeded.

@bzz suggested

to add TravisCI cache to something under GOPATH, to reduce the probability of hitting this due to network failure?