Prompt-multiline jumps to the bottom of the screen on first character insertion

[jmcken8]

Minimal repro case (mac OSX):

#include "cpp-terminal/exception.hpp"
#include "cpp-terminal/key.hpp"
#include "cpp-terminal/prompt.hpp"
#include "cpp-terminal/terminal.hpp"
#include "cpp-terminal/tty.hpp"
#include <cpp-terminal/terminal_initializer.hpp>
#include <iostream>

bool determine_completeness(const std::string& command)
{
  // Determine if the statement is complete
  if (command.size() > 1 && command.substr(command.size() - 2, 1) == "\\")
    return false;
  return true;
}
int main()
{
  try
  {
    Term::terminal.setOptions(Term::Option::NoClearScreen,
                              Term::Option::SignalKeys,
                              Term::Option::NoCursor,
                              Term::Option::Raw);
    if (!Term::is_stdin_a_tty())
    {
      throw Term::Exception("The terminal is not attached to a TTY and therefore can't "
                            "catch user input. Exiting...");
    }
    Term::cout << "Interactive prompt.\n"
               << "  * Use Ctrl-D to exit.\n"
               << "  * Use Enter to submit.\n"
               << "  * Features:\n"
               << "    - Editing (Keys: Left, Right, Home, End, Backspace)\n"
               << "    - History (Keys: Up, Down)" << std::endl;
               std::vector<std::string> history;
               std::function<bool(std::string)> iscomplete = determine_completeness;
    std::string input = Term::prompt_multiline("Query> ", history, iscomplete);
    return 0;
  }
  catch (const Term::Exception& re)
  {
    std::cerr << "cpp-terminal error: " << re.what() << std::endl;
    return 2;
  }
  return 0;
}

Then clear the terminal and run.

I think I see what the issue is, I'll post a PR.