travis: add `go test -i ./...` to install test dependencies
travis: add `go test -i ./...` to install test dependencies

(needed because of `go/importer` which is used in the tests).

sourcegraph/go-langserver,lambdalab/go-langserver,lambdalab/go-langserver,sourcegraph/go-langserver,sourcegraph/go-langserver,lambdalab/go-langserver