chore(package): update assume to version 2.2.0

Closes #13

Author: greenkeeper[bot]

package.json

@@ -19,7 +19,7 @@
     "axo": "0.0.x"
   },
   "devDependencies": {
-    "assume": "~1.5.0",
+    "assume": "~2.2.0",
     "istanbul": "~0.4.5",
     "mocha": "~4.1.0",
     "pre-commit": "~1.2.0"