fix(eslint): use 'npx eslint' when local binary is missing

[markuskreukniet]

Fixes #747
Resolves #747
Closes #747

Description

This fixes an issue where nvim-lint fails to find ESLint if it's not installed globally.

• Previously, the command used "eslint", which fails if it's not in PATH.
• Now, it falls back to "npx eslint", which correctly finds either the local or global version.

Why This Fix?

• npx eslint works even if eslint is not globally installed.
• This prevents silent failures and makes nvim-lint more reliable.