Correct manifest extension (manifest-file-extension)

manifest-file-extension warns against using non-standard file
extensions for the [web app manifest][spec] file.

Why is this important?

While the [.webmanifest][file extension] file extension is not
enforced by the specification, nor is it required by browsers, using
it makes it:

* [easier to set custom server configurations][server configs] for
the web app manifest file
* possible to benefit from [existing configurations][other configs]

What does the hint check?

The hint checks if the recommended [.webmanifest][file extension]
file extension is used for the web app manifest file.

$3

``html

`

`html

`

$3

`html

`

How to use this hint?

This package is installed automatically by webhint:

`bash
npm install hint --save-dev
`

To use it, activate it via the [.hintrc][hintrc] configuration file:

`json
{
"connector": {...},
"formatters": [...],
"hints": {
"manifest-file-extension": "error",
...
},
"parsers": [...],
...
}
`

Note: The recommended way of running webhint is as a devDependency` of
your project.

Further Reading

* [Web App Manifest Specification][spec]

[file extension]: https://w3c.github.io/manifest/#media-type-registration
[other configs]: https://github.com/jshttp/mime-db/blob/67a4d013c31e73c47b5d975062f0088aea6cd5cd/src/custom-types.json#L85-L92
[server configs]: https://github.com/w3c/manifest/issues/346
[hintrc]: https://webhint.io/docs/user-guide/configuring-webhint/summary/
[spec]: https://www.w3.org/TR/appmanifest