Install exponential-backoff

This library seems to be used in other parts of the repo.
Thus, it makes sense to stick to it in this case as well,
to keep things consistent.

Author: Zloka

npm-shrinkwrap.json

@@ -127,6 +127,7 @@
     "deep-equal-in-any-order": "^2.0.6",
     "exegesis": "^4.2.0",
     "exegesis-express": "^4.0.0",
+    "exponential-backoff": "^3.1.2",
     "express": "^4.16.4",
     "filesize": "^6.1.0",
     "form-data": "^4.0.1",