Use rubocop

[utkarsh2102]

Hi @ai,

Thanks again for your awesome work in maintaining this! 🔥

As discussed in #164, here's the first follow-up on this.
I'll do all the changes in 3 or 4 parts :)
(sorry for the delay, though!)

Signed-off-by: Utkarsh Gupta <utkarsh@debian.org>

[ai]

Too late. I just deprecate the whole Autoprefixer Rails b01fef4

[utkarsh2102]

Woops :/
However, given that there are so many gems using this already, we will keep maintaining this in Debian for a while, at least!

It'd still be nice if you could integrate these changes :)

[utkarsh2102]

Well, in case you think it's not worth doing this anymore, I have one minor thing to change here - dropping the use of git ls-files in gemspec. This should really help us in maintaining. So I can instead shape this PR to do that instead?

Or in case you think, it's okay to use rubocop here, still, I can complete this whole thing.

Let me know what you think.

[ai]

Yeap, I will continue to accept security PRs.

I will accept Robocop PR a little later and I am open for gemspec PR too.

[utkarsh2102]

Okay, that's very great of you!
Thanks for your work, really! Let me know when you think it's time for merging this. Once done, I'll open another follow-up PR for RuboCop fixes and lastly for gemspec!

Thanks again! ❤️