Update QUnit dependency to fix test failure

The 'createVault() fails if directory exists' test
return a promise which resolved to [null], this triggered
a bug in QUnitJS when handling tests that return a promise.

See qunitjs/qunit#844 (comment)

package.json

@@ -13,7 +13,7 @@
     "jpm": "0.0.13",
     "jsdom": "^5.6.1",
     "module-deps": "^3.5.6",
-    "qunitjs": "^1.16.0",
+    "qunitjs": "^1.19.0",
     "sort-stream": "^1.0.1",
     "tsd": "^0.6.0-beta.5",
     "tslint": "^2.4.5",