Add coverage script

Author: BridgeAR

package.json

@@ -20,7 +20,8 @@
   "scripts": {
     "test": "standard && tap test.js",
     "benchmark": "node benchmark.js",
-    "compare": "node compare.js"
+    "compare": "node compare.js",
+    "coverage": "nyc --reporter=html --reporter=text npm test"
   },
   "author": "Ruben Bridgewater",
   "license": "MIT",
@@ -36,6 +37,7 @@
     "json-stable-stringify": "^1.0.1",
     "json-stringify-deterministic": "^1.0.1",
     "json-stringify-safe": "^5.0.1",
+    "nyc": "^13.0.1",
     "standard": "^11.0.0-beta.0",
     "tap": "^11.0.0"
   },