chore(package): update memdown to version 5.1.0

Closes #27

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
     "browserify": "^14.1.0",
     "chai": "^3.5.0",
     "istanbul": "^0.4.5",
-    "memdown": "^1.0.0",
+    "memdown": "^5.1.0",
     "mocha": "^3.2.0",
     "pouchdb": "^6.0.0"
   }