Generate human readable IDs for client URLs

Based on @FranzSkuffka's suggested enhancement in PR 207 on
localtunnel/localtunnel
(https://github.com/localtunnel/localtunnel/pull/207), this PR uses the
"human-readable-ids" package to generate IDs of the form
"adjective-noun-number". These IDs are easier to remember and arguably
more useful in testing since they can be retyped without copying and
pasting.

Some sample IDs generated by this package are:

* heavy-puma-90
* grump-walrus-64
* purple-starfish-58
* nasty-seahorse-9

package.json

@@ -14,6 +14,7 @@
     "bluebird": "3.5.1",
     "book": "1.3.3",
     "debug": "3.1.0",
+    "human-readable-ids": "1.0.3",
     "koa": "2.4.1",
     "localenv": "0.2.2",
     "on-finished": "2.3.0",