tokens: Add a new createToken with customerId

Sources/API/Routes/TokenRoutes.swift

@@ -149,6 +149,18 @@ public final class TokenRoutes {
         return try StripeRequest(client: self.client, method: .post, route: .tokens, body: Body.data(body.formURLEncoded()), headers: nil)
     }
 
+    /**
+     Create a payment token from a customer
+
+     - parameter withCustomerId: The customer ID to generate the token with
+
+     - returns: A StripeRequest<> item which you can then use to convert to the corresponding node
+     */
+    public func createToken(withCustomerId customerId: String) throws -> StripeRequest<Token> {
+        let body = try Node(node: ["customer": customerId])
+        return try StripeRequest(client: self.client, method: .post, route: .tokens, body: Body.data(body.formURLEncoded()))
+    }
+
     /**
      Retrieve a token
      Retrieves the token with the given ID.