docs(alumn): add Jay Phelps as core team alumn (#5262)

Author: jayphelps

docs_app/content/marketing/contributors.json

@@ -121,6 +121,15 @@
     "website": "http://staltz.com",
     "group": "Alumn"
   },
+  "jay": {
+    "name": "Jay Phelps",
+    "role": "Developer",
+    "github": "https://github.com/jayphelps",
+    "picture": "https://avatars0.githubusercontent.com/u/762949",
+    "twitter": "https://twitter.com/_jayphelps",
+    "website": "http://jayphelps.com",
+    "group": "Alumn"
+  },
   "nat": {
     "name": "Natalie Smith",
     "role": "Developer",