Update `mocha` to latest version

According to Maxim Kadushkin mocha tests was added long time ago
and not maintained.
So may to remove all togher, but for now - just update to latest.

build/package.json

@@ -8,7 +8,7 @@
     "grunt": "^1.0.0",
     "grunt-replace": "^1.0.0",
     "grunt-text-replace": "0.3.11",
-    "mocha": "1.18.2",
+    "mocha": "^3.0.0",
     "chai": "1.9.1",
     "grunt-mocha": "^1.0.0",
     "grunt-jscoverage": "0.1.1",