Add support for `yaml` and `yml` theme's extension

[JuanVqz]

Describe the bug

If you add a theme with yaml extension it will fail.

To Reproduce

Steps to reproduce the behavior:

1. Installation

   • [x] I installed it via npm i -g alacritty-themes (global installation)

2. Add a theme with YAML extension

3. Run alacritty-themes

   I type "alacritty-themes Fedora"

4. See error

Expected behavior

Add support to yaml and yaml extensions

Operating System:

• [ ] Windows
• [ ] Ubuntu
• [ ] Pop Os
• [ ] Arch
• [ ] Other, which one?

Add your alacritty.yml content

# your alacritty content here

Screenshots

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