Update droplets.go

Co-authored-by: Andrew Starr-Bochicchio <andrewsomething@users.noreply.github.com>

droplets.go

@@ -654,7 +654,7 @@ type dropletBackupPolicyRoot struct {
 }
 
 type dropletBackupPoliciesRoot struct {
-	DropletBackupPolicies []*DropletBackupPolicy `json:"policies,omitempty"`
+	DropletBackupPolicies map[int]*DropletBackupPolicy `json:"policies,omitempty"`
 	Links                 *Links                 `json:"links,omitempty"`
 	Meta                  *Meta                  `json:"meta"`
 }