Update dependencies, enable pruning for vendor/

So, `dep` got an nice new feature to remove tests and non-go files from
`vendor/`, and this brings the size of the vendor directory from ~300MiB
down to ~20MiB. We don that now.

vendor/github.com/minio/minio-go/utils.go

@@ -222,6 +222,7 @@ var supportedHeaders = []string{
 	"content-encoding",
 	"content-disposition",
 	"content-language",
+	"x-amz-website-redirect-location",
 	// Add more supported headers here.
 }