travis: add go_import_path

Change-Id: I3062f23e143916f0c87ec0a043f0682b8c01612a
Reviewed-on: https://go-review.googlesource.com/c/141597
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Author: zchee

.travis.yml

@@ -6,6 +6,8 @@ go:
   - 1.9.x
   - master
 
+go_import_path: golang.org/x/lint
+
 install:
   - go get -t -v ./...