LinkedIn Sharer-URL to 2020 Version

[NoNamePro0]

Updates the Sharer-URL to 2020 Version.

Currently: https://www.linkedin.com/shareArticle?url={url}&title={title}&summary={text}&source={provider}
2020 Version (This PR): https://www.linkedin.com/sharing/share-offsite/?url={url}

This pull request will fix #378.

More information

[richard67]

Seems to be correct according to https:/bradvin/social-share-urls#linkedin.

[richard67]

@compeak I haven't tested if sharing works because I'm not at LinkedIn, but I've tested that a dialog for singning in or up to LinkedIn appears, and the URL to be linked it passed to it.

In additon I've checked at https://stackoverflow.com/questions/10713542/how-to-make-a-custom-linkedin-share-button/61583006#61583006 and https://docs.microsoft.com/en-us/linkedin/consumer/integrations/self-serve/plugins/share-plugin that it's true that there is only the URL parameter supported. These sources and the info on https:/bradvin/social-share-urls#linkedin are up to date.

So I think it's ok to merge this PR.