build: don't fetch dependencies in TravisCI; they should be vendored

Change-Id: Ib7560a3ddfca6d6f423aadb8ad0c1a6fe739fcf8
Reviewed-on: https://upspin-review.googlesource.com/15240
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/.travis.yml b/.travis.yml
index 8c5a285..029907a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,6 +2,7 @@
 go:
 - 1.9.x
 go_import_path: gcp.upspin.io
+install: true
 script: go test -short -race ./...
 notifications:
   email: