streams2: Set Readable lwm to 0 by default

lib/_stream_readable.js

@@ -46,7 +46,7 @@ function ReadableState(options, stream) {
   // the minimum number of bytes to buffer before emitting 'readable'
   // default to pushing everything out as fast as possible.
   this.lowWaterMark = options.hasOwnProperty('lowWaterMark') ?
-      options.lowWaterMark : 1024;
+      options.lowWaterMark : 0;
 
   // cast to ints.
   assert(typeof this.bufferSize === 'number');