Support fetching the latest develop build

Frustratingly, this requires a buildkite API token, even though
the builds & artifacts are available without auth on the buildkite
website.

package.json

@@ -46,7 +46,6 @@
     "eslint-config-google": "^0.7.1",
     "eslint-plugin-babel": "^4.1.2",
     "find-npm-prefix": "^1.0.2",
-    "follow-redirects": "^1.9.0",
     "fs-extra": "^8.1.0",
     "glob": "^7.1.6",
     "matrix-js-sdk": "^2.4.6-rc.1",