use go 1.12

Signed-off-by: hongming <talonwan@yunify.com>

vendor/github.com/gregjones/httpcache/.travis.yml

@@ -1,18 +1,18 @@
 sudo: false
 language: go
+go:
+  - 1.6.x
+  - 1.7.x
+  - 1.8.x
+  - master
 matrix:
   allow_failures:
     - go: master
   fast_finish: true
-  include:
-    - go: 1.10.x
-    - go: 1.11.x
-      env: GOFMT=1
-    - go: master
 install:
   - # Do nothing. This is needed to prevent default install action "go get -t -v ./..." from happening here (we want it to happen inside script step).
 script:
   - go get -t -v ./...
-  - if test -n "${GOFMT}"; then gofmt -w -s . && git diff --exit-code; fi
+  - diff -u <(echo -n) <(gofmt -d .)
   - go tool vet .
   - go test -v -race ./...