nits: Fix accidental link to Behat/Behat contributors

Copied-and-pasted from the Behat readme, but this should obviously link
to Behat/Gherkin.

Author: acoulton

README.md

@@ -59,7 +59,7 @@ Contributors
 - Andrew Coulton [acoulton](https://github.com/acoulton) [current maintainer]
 - Carlos Granados [carlos-granados](https://github.com/carlos-granados) [current maintainer]
 - Christophe Coevoet [stof](https://github.com/stof) [current maintainer]
-- Other [awesome developers](https://github.com/Behat/Behat/graphs/contributors)
+- Other [awesome developers](https://github.com/Behat/Gherkin/graphs/contributors)
 
 Support the project
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