User `name` instead of `property` for Twitter

[tordans]

Facebook uses property, but twitter specifies name`.

See https://developer.twitter.com/en/docs/twitter-for-websites/cards/guides/getting-started#opengraph

Open Graph protocol also specifies the use of property and content attributes for markup (<meta property="og:image" content="http://example.com/ogp.jpg"/>) while Twitter cards use name and content.

Or for example the "Sample Code" for the Summary Card https://developer.twitter.com/en/docs/twitter-for-websites/cards/overview/summary

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This was initially added in https://github.com/jekyll/jekyll-seo-tag/commit/78984897361bc9baeeaf840c5073493104ee0e7e