fix #75: detect sass binary in the path and use it if available

[drupol]

This PR fix #75 by doing:

• Use the binary sass if it is available in the path
• If the path is not available in the path, it will try to download it

[bocharsky-bw]

Hm, correct me if I'm wrong but you're trying to prioritize the binary from paths among other available binaries. I see this bundle allows to specify the path to the binary you want to use, see: https://symfony.com/bundles/SassBundle/current/index.html#using-a-different-binary - so it already works the way you need, i.e. you can just specify the path to the local binary from path and it will work for you, right? The only problem with this behaviour is that you need to specify that path manually. In case we want to automate it - we need to follow the next logic IMO:

1. Check if the binary path is set in the config, i.e. symfonycasts_sass.binary option. if it's set - just use it, no need to find anything because it's explicitly configured
2. If no symfonycasts_sass.binary option is set - try to find the installed binary from the path as you suggest. If found - use it.
3. If no installed binary in the path - try to download the latest binary.

[drupol]

OK will adjust my PR then ! Thank you for the review!

[bocharsky-bw]

Also, tests and code styles were fixed in #73 , please, release your PR

[drupol]

@bocharsky-bw Ready for another review.

[bocharsky-bw]

This looks good to me now, thanks for this idea!