Pin randombytes to version 2.0.1.

Version 2.0.2 was published today, but causes tests to fail in browser
with "RangeError: Trying to access beyond buffer length".  I don't
understand what that error is about, but it seems fine to pin to the
previous version.

Change-Id: I96aea86dba1bf26e94225f47c4a45e49eaa34610
diff --git a/package.json b/package.json
index 452413a..3c5968f 100644
--- a/package.json
+++ b/package.json
@@ -13,7 +13,7 @@
     "es6-shim": "^0.20.2",
     "inherits": "~2.0.1",
     "format": "~0.2.1",
-    "randombytes": "~2.0.1",
+    "randombytes": "2.0.1",
     "domready": "~1.0.7",
     "es6-promise": "~2.1.1"
   },