Add selection color

[louie-github]

If you're reporting an UI issue, make sure you take a screenshot that shows the actual bug.
In the most recent release of Alacritty on June 1, the alacritty.yml file now has selection color options:

  ...
  #  cursor: '#ffffff'

  # Selection colors
  #
  # Colors which should be used to draw the selection area. If selection
  # background is unset, selection color will be the inverse of the cell colors.
  # If only text is unset the cell text color will remain the same.
  #selection:
  #  text: '#eaeaea'
  #  background: '#404040'

  # Normal colors
  ...

I've created pull request #5 to simply add the selection colors into dracula.yml:

  selection:
    text: '0xf8f8f2'
    background: '0x44475a'

I might be getting something wrong with the colors though. Correct me if they're not accurate with the specification.