go mod and vendor changes

vendor/github.com/mitchellh/copystructure/README.md

@@ -0,0 +1,21 @@
+# copystructure
+
+copystructure is a Go library for deep copying values in Go.
+
+This allows you to copy Go values that may contain reference values
+such as maps, slices, or pointers, and copy their data as well instead
+of just their references.
+
+## Installation
+
+Standard `go get`:
+
+```
+$ go get github.com/mitchellh/copystructure
+```
+
+## Usage & Example
+
+For usage and examples see the [Godoc](http://godoc.org/github.com/mitchellh/copystructure).
+
+The `Copy` function has examples associated with it there.