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/constants.go

@@ -27,10 +27,6 @@ const absMinPartSize = 1024 * 1024 * 5
 // putObject behaves internally as multipart.
 const minPartSize = 1024 * 1024 * 64
 
-// copyPartSize - default (and maximum) part size to copy in a
-// copy-object request (5GiB)
-const copyPartSize = 1024 * 1024 * 1024 * 5
-
 // maxPartsCount - maximum number of parts for a single multipart session.
 const maxPartsCount = 10000
 
@@ -61,3 +57,6 @@ const (
 
 // Storage class header constant.
 const amzStorageClass = "X-Amz-Storage-Class"
+
+// Website redirect location header constant
+const amzWebsiteRedirectLocation = "X-Amz-Website-Redirect-Location"