vendor: update github.com/spf13/cobra to master

vendor/github.com/spf13/cobra/.travis.yml

@@ -2,9 +2,11 @@ language: go
 
 matrix:
   include:
-    - go: 1.9.4
-    - go: 1.10.0
+    - go: 1.10.x
+    - go: 1.11.x
     - go: tip
+    - go: 1.11.x
+      script: diff -u <(echo -n) <(gofmt -d -s .)
   allow_failures:
     - go: tip
 
@@ -15,7 +17,6 @@ before_install:
 script:
   - PATH=$PATH:$PWD/bin go test -v ./...
   - go build
-  - diff -u <(echo -n) <(gofmt -d -s .)
   - if [ -z $NOVET ]; then
       diff -u <(echo -n) <(go tool vet . 2>&1 | grep -vE 'ExampleCommand|bash_completions.*Fprint');
     fi