Upgrading the plugins packages to be compatible with the new Grapesjs Version

[kanaihyakumar]

There are two packages which still outdated due to which there is an issue. It will be really great if anyone upgrade the below plugins to be compatible with the newer version:

1. parser-postcss
2. style-gradient

Thank you in advance

[artf]

@kanaihyakumar I'll be happy to merge PRs with the updates

[kanaihyakumar]

Thank you for the response. I have raised a pull request with changes it needed. If u merge it will be great.