go.mod: github.com/spf13/cobra v1.6.1

We were using v1.0.0 of Cobra as newer versions added spf13/viper as dependency,
which came with many indirect dependencies. Cobra v1.6.0 and up no longer depend
on viper, so we can now safely upgrade to the latest version.

full diff: https://github.com/spf13/cobra/compare/v1.0.0...v1.6.1

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

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

@@ -3,8 +3,9 @@ sudo: false
 language: go
 
 go:
-  - 1.7.3
-  - 1.8.1
+  - 1.9.x
+  - 1.10.x
+  - 1.11.x
   - tip
 
 matrix:
@@ -12,7 +13,7 @@ matrix:
     - go: tip
 
 install:
-  - go get github.com/golang/lint/golint
+  - go get golang.org/x/lint/golint
   - export PATH=$GOPATH/bin:$PATH
   - go install ./...