chore(package): update documentation to version 12.1.4

Closes #206

Author: greenkeeper[bot]

Diff for: package.json

@@ -38,7 +38,7 @@
   "devDependencies": {
     "coveralls": "^3.0.1",
     "dfinity-radix-tree": "^0.2.5",
-    "documentation": "^8.0.0",
+    "documentation": "^12.1.4",
     "level-browserify": "^1.1.2",
     "nyc": "^12.0.2",
     "standard": "11.0.1",