Upgrade standard devDependency from ^12.0.0 to ^13.0.1 (#151)

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
     "level-community": "^3.0.0",
     "nyc": "^14.0.0",
     "pinkie": "^2.0.4",
-    "standard": "^12.0.0",
+    "standard": "^13.0.1",
     "tape": "^4.2.2",
     "uuid": "^3.3.2",
     "verify-travis-appveyor": "^3.0.0"