Apply no-buffer-constructor lint rule

lib/auth.js

@@ -54,7 +54,7 @@ function parseAuthHeader(authHeader) {
 }
 
 function basic(username, password) {
-  return "Basic " + new Buffer(`${username}:${password}`).toString("base64");
+  return "Basic " + Buffer.from(`${username}:${password}`).toString("base64");
 }
 
 function digest(username, password, uri, httpMethod, body, authHeader) {