tests: use assert instead of should

Author: dougwilson

package.json

@@ -18,8 +18,7 @@
     "benchmark": "1.0.0",
     "beautify-benchmark": "0.2.4",
     "istanbul": "0.3.2",
-    "mocha": "~1.21.5",
-    "should": "~4.0.0"
+    "mocha": "~1.21.5"
   },
   "files": [
     "LICENSE",