yml/file-extension 
enforce YAML file extension
📖 Rule Details 
This rule aims to enforce YAML file extension.
🔧 Options 
yaml
yml/file-extension:
  - error
  - extension: yaml # or 'yml'
    caseSensitive: true- extension... The extension you want to enforce. Default is- "yaml".
- caseSensitive... Specify- trueto enforce lowercase extension. Default is- true.
🚀 Version 
This rule was introduced in eslint-plugin-yml v1.2.0