Merge pull request facebook#17 from Level/greenkeeper/abstract-leveldown-2.7.0

Update abstract-leveldown to the latest version 🚀

Author: ralphtheninja

package.json

@@ -30,7 +30,7 @@
   ],
   "main": "leveldown.js",
   "dependencies": {
-    "abstract-leveldown": "~2.6.1",
+    "abstract-leveldown": "~2.7.0",
     "bindings": "~1.3.0",
     "fast-future": "~1.0.2",
     "nan": "~2.7.0",