message: [web-service] include prompt when searching for `Done`
diff: @@ -195,7 +195,7 @@ char *OpenThreadClient::Execute(const char *aFormat, ...)
  rxLength += count;
  mBuffer[rxLength] = '\0';
  - done = strstr(mBuffer, "Done\r\n");
  + done = strstr(mBuffer, "Done\r\n> ");
  if (done != nullptr)
  {
  