Automatically update url and sha256 of NeoVim on Formula file

[pantuza]

Description

This Pull Request has a script to update NeoVim url and sha256 inside
formula file. For that, it checks current version from CMakeLists.txt file at
neovim repository, compute sha256 and updates formula.

How to use

To update formula, you should run:

$> ./scripts/formula-version.sh

The script only updates formula if there is a new version of tarball at github arquive.

How it works

First, we clone or update neovim and homebrew-neovim repositories.
Then, we check for current version and tarball at github arquive.
After, we compute the sha256 and compare with current one.
Then, update formula file if necessary adding new arquive url and computed sha256.

Considerations

The Pull request come from part of a task described at this issue.

ps: Script tested on Linux. Some tools like sed works differently is OS X, for example.

[justinmk]

Thanks for this. Didn't find the time to test this. The formula is now maintained by homebrew core: https://github.com/Homebrew/homebrew-core/blob/master/Formula/neovim.rb