postmarketos-ui-sway: change default terminal

(Original issue title: postmarketos-ui-sway: alacritty: Failed to initialize any backend)

Describe your issue

What's the expected behaviour?

Pressing super + Return should open a new terminal

What's the current behaviour?

Nothing happens.

How to reproduce your issue?

Install postmarketos-ui-sway

What device are you using?

pine64-rockpro64

On what postmarketOS version did you encounter the issue?

• edge (master branch)
• stable (v20.05 branch)

On what environment did you encounter the issue?

Phone environments

• Phosh
• Plasma Mobile
• Sxmo

Other

• No environment
• GNOME
• KDE Plasma
• Kodi
• MATE
• Shelli
• Sway
• Weston
• Xfce4
• fbkeyboard
• i3wm

How did you get postmarketOS image?

• from https://images.postmarketos.org
• I built it using pmbootstrap
• It was preinstalled on my device

What's the build date of the image? (in yyyy-mm-dd format)

2021-02-23

Additional information

thread 'main' panicked at 'Failed to initialize any backend! Wayland status: NoCompositorListening X11 status: XOpenDisplayFailed', /home/bui
ldozer/aports/community/alacritty/src/cargo/registry/src/github.com-1ecc6299db9ec823/winit-0.24.0/src/platform_impl/linux/mod.rs:605:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace