docs: add corehtml5canvas as a contributor (testing-library#655)

* docs: add corehtml5canvas as a contributor * Update URL for corehtml5canvas's site manually

Author: nickserv

.all-contributorsrc

@@ -1046,6 +1046,15 @@
  "contributions": [
  "doc"
  ]
+ },
+ {
+ "login": "corehtml5canvas",
+ "name": "Core HTML5 Canvas, the book",
+ "avatar_url": "https://avatars1.githubusercontent.com/u/1553693?v=4",
+ "profile": "http://gearysite.com/",
+ "contributions": [
+ "doc"
+ ]
  }
  ],
  "contributorsPerLine": 7,