[minor] Allow to write frames with up to 2^48 - 1 bytes of data (#1973)

Author: prettydiff

lib/sender.js

@@ -75,8 +75,9 @@ class Sender {
     if (payloadLength === 126) {
       target.writeUInt16BE(data.length, 2);
     } else if (payloadLength === 127) {
-      target.writeUInt32BE(0, 2);
-      target.writeUInt32BE(data.length, 6);
+      target[2] = 0;
+      target[3] = 0;
+      target.writeUIntBE(data.length, 4, 6);
     }
 
     if (!options.mask) return [target, data];