Fix calculation of final drawBit in drawVerticalLine

[igrr]

Bitwise "and" has lower precedence than shift, so calculation of drawBit was not working the way it was intended, resulting in the following output (left). Correct output is on the right.

Test case:

  display.clear();
  int x = 4;
  const int y0 = 16;
  for (int length = 1; length <= 32; ++length) {
    display.drawVerticalLine(x, y0, length);
    ++x;
  }
  display.display();

[FWeinb]

Very good catch, thanks for fixing it!