Add support for iCalendar (ics)

[sripreddyg]

If you're adding support for a new file type, please follow the below steps:

• Add a fixture file named fixture.<extension> to the fixture directory.
• Add the file extension to the types array in test.js.
• Add the file type detection logic to the index.js file.
• Add the file extension to the Supported file types section in the readme, in the format - [`<extension>`](URL) - Format name, for example, - [`png`](https://en.wikipedia.org/wiki/Portable_Network_Graphics) - Portable Network Graphics
• Add the file extension to the keywords array in the package.json file.
• Run $ npm test to ensure the tests pass.
• Open a pull request with a little like Add support for Format, for example, Add support for PNG.
• The pull request description should include a link to the official page of the file format or some other source. Also include a link to where you found the file type detection / magic bytes.

[ThomPattersonNM]

Looks good to me. Only thing you may want to add is the ics keyword in package.json.

[MaxLeiter]

I know nothing of the iCalendar standard, but https://icalendar.org/validator.html returns some (9) errors in the fixture file. May be worth looking into.

[ghost]

Looks good to me, it doesn't appear to obviously introduce any vulnerabilities, and Checkmarx scan of this branch comes back clean.

[sindresorhus]

@sripreddyg Can you make sure the fixture correctly passes https://icalendar.org/validator.html?

[sindresorhus]

Open a pull request with a little like Add support for Format, for example, Add support for PNG.

Not followed.

The pull request description should include a link to the official page of the file format or some other source. Also include a link to where you found the file type detection / magic bytes.

Not followed.

[sripreddyg]

@sindresorhus Thanks for suggestions, I have fixed it. please review and approve if you are good with change