Require nodeunit 0.9.0

Bump the nodeunit version requirement in order to get this fix [0] for
running with node 0.11 and later.

[0] caolan/nodeunit@5ba1a94

Author: sunfishcode

package.json

@@ -17,7 +17,7 @@
     "pattern-match": "0.3.0"
   },
   "devDependencies": {
-    "nodeunit": "0.7.4"
+    "nodeunit": "0.9.0"
   },
   "directories": {
     "lib": "./lib"