backport env variable change

Author: calvinmetcalf

readable.js

@@ -6,3 +6,6 @@ exports.Writable = require('./lib/_stream_writable.js');
 exports.Duplex = require('./lib/_stream_duplex.js');
 exports.Transform = require('./lib/_stream_transform.js');
 exports.PassThrough = require('./lib/_stream_passthrough.js');
+if (!process.browser && process.env.READABLE_STREAM === 'disable') {
+  module.exports = require('stream');
+}