Update events to v2

Matches the Node 8 API. v1 matched Node 4, and some new methods have
since been introduced (notably `prepend[Once]Listener`).

The major bump in `events` was because:

 - There is a breaking change in the `listeners()` method regarding
   `once()` listeners nodejs/node#6881
   I think it's super unlikely to affect anyone, but there you go.
 - The gzipped size almost doubled from 1.1KB to 2.1KB. It'll shrink a
   bit because some patches have since landed in Node that remove some
   code, but it'll still be bigger than it was because of the new
   methods.

Deets:
https://github.com/Gozala/events/releases/tag/v2.0.0

package.json

@@ -15,7 +15,7 @@
     "constants-browserify": "^1.0.0",
     "crypto-browserify": "^3.11.0",
     "domain-browser": "^1.1.1",
-    "events": "^1.0.0",
+    "events": "^2.0.0",
     "https-browserify": "^1.0.0",
     "os-browserify": "^0.3.0",
     "path-browserify": "0.0.0",