chore(package): update assume to version 2.1.0

Author: greenkeeper[bot]

package.json

@@ -35,7 +35,7 @@
     "which": "1.2.x"
   },
   "devDependencies": {
-    "assume": "~1.5.0",
+    "assume": "~2.1.0",
     "istanbul": "0.4.x",
     "mocha": "~3.3.0",
     "pre-commit": "git://github.com/observing/pre-commit.git"