chore(package): update jest to version 21.0.0

Closes #13

Author: greenkeeper[bot]

package.json

@@ -41,6 +41,6 @@
     "eslint": "^3.12.2",
     "eslint-config-airbnb-base": "^11.0.0",
     "eslint-plugin-import": "^2.2.0",
-    "jest": "^19.0.1"
+    "jest": "^21.0.0"
   }
 }