Upgrade hcl to v2

Signed-off-by: Patrick Van Stee <patrick@vanstee.me>

vendor/github.com/zclconf/go-cty/cty/collection.go

@@ -0,0 +1,34 @@
+package cty
+
+import (
+	"errors"
+)
+
+type collectionTypeImpl interface {
+	ElementType() Type
+}
+
+// IsCollectionType returns true if the given type supports the operations
+// that are defined for all collection types.
+func (t Type) IsCollectionType() bool {
+	_, ok := t.typeImpl.(collectionTypeImpl)
+	return ok
+}
+
+// ElementType returns the element type of the receiver if it is a collection
+// type, or panics if it is not. Use IsCollectionType first to test whether
+// this method will succeed.
+func (t Type) ElementType() Type {
+	if ct, ok := t.typeImpl.(collectionTypeImpl); ok {
+		return ct.ElementType()
+	}
+	panic(errors.New("not a collection type"))
+}
+
+// ElementCallback is a callback type used for iterating over elements of
+// collections and attributes of objects.
+//
+// The types of key and value depend on what type is being iterated over.
+// Return true to stop iterating after the current element, or false to
+// continue iterating.
+type ElementCallback func(key Value, val Value) (stop bool)