[microscript] keyboard.press not updated unless update is defined

`keyboard.press` (but not `keyboard`) will be unresponsive to input unless `update` is defined (as anything)

will not work:
```lua
draw = function()
  if keyboard.press.SPACE then
    print('spacebar was pressed')
  end
end
```

will work:
```lua
update = 0

draw = function()
  if keyboard.press.SPACE then
    print('spacebar was pressed')
  end
end
```