message: Fix readme logo icon URL
diff: <p align="center">
  - <img width="200" alt="Alacritty Logo" src="extra/logo/compat/alacritty-term+scanlines.png">
  + <img width="200" alt="Alacritty Logo" src="https://raw.githubusercontent.com/alacritty/alacritty/master/extra/logo/compat/alacritty-term%2Bscanlines.png">
  </p>
  <h1 align="center">Alacritty - A fast, cross-platform, OpenGL terminal emulator</h1>
  