Fix signMessage serialization.

Author: justmoon

src/message.js

@@ -38,7 +38,7 @@ Bitcoin.Message = (function () {
  if (compressed) i += 4;
 
  var rBa = obj.r.toByteArrayUnsigned();
- var sBa = obj.r.toByteArrayUnsigned();
+ var sBa = obj.s.toByteArrayUnsigned();
 
  // Pad to 32 bytes per value
  while (rBa.length < 32) rBa.unshift(0);