chore(package): update documentation to version 8.1.0

Closes #9

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
   },
   "devDependencies": {
     "coveralls": "^3.0.0",
-    "documentation": "^6.0.0",
+    "documentation": "^8.1.0",
     "nyc": "^11.3.0",
     "standard": "^11.0.0",
     "tape": "^4.0.3"