fix: Add server-side proxy support via fetch-with-proxy (#2044)

* fix: Add server-side proxy support via fetch-with-proxy

closes #1893

For some fun discussion on why this is required, see this issue: https://github.com/nodejs/node/issues/8381

* lint

server/utils/avatars.js

@@ -1,6 +1,6 @@
 // @flow
 import crypto from "crypto";
-import fetch from "isomorphic-fetch";
+import fetch from "fetch-with-proxy";
 
 export const DEFAULT_AVATAR_HOST = "https://tiley.herokuapp.com";