Add gatsby-source-behance to plugins list (gatsbyjs#3465)

Author: LekoArts

docs/docs/plugins.md

@@ -159,6 +159,7 @@ root.
 * [gatsby-remark-graph](https://github.com/konsumer/gatsby-remark-graph)
 * [gatsby-remark-sequence](https://github.com/liudonghua123/gatsby-remark-sequence)
 * [gatsby-source-airtable](https://github.com/kevzettler/gatsby-source-airtable)
+* [gatsby-source-behance](https://github.com/LeKoArts/gatsby-source-behance)
 * [gatsby-source-datocms](https://github.com/datocms/gatsby-source-datocms)
 * [gatsby-source-github](https://github.com/mosch/gatsby-source-github)
 * [gatsby-source-google-sheets](https://github.com/brandonmp/gatsby-source-google-sheets)