Use nyc instead of istanbul

Author: SimenB

.gitignore

@@ -4,4 +4,5 @@
 *.iml
 
 coverage/
+.nyc_output/
 test-output.xml

package.json

@@ -20,16 +20,17 @@
     "eslint-config-standard": "^6.0.0-beta.2",
     "eslint-plugin-promise": "^2.0.1",
     "eslint-plugin-standard": "^2.0.0",
-    "istanbul": "^0.4.4",
     "mocha": "^3.0.2",
     "node-version-check": "^2.1.0",
+    "nyc": "^7.1.0",
     "rimraf": "^2.5.4",
     "should": "^11.0.0",
     "sinon": "^1.17.5"
   },
   "scripts": {
-    "clean": "rimraf coverage/",
-    "cover": "istanbul cover _mocha",
+    "clean": "rimraf coverage/ .nyc_output/",
+    "cover": "nyc mocha",
+    "postcover": "nyc report --reporter lcov",
     "lint": "node-version-gte-4 && eslint index.js test/main.js || node-version-lt-4",
     "precover": "npm run lint && npm run clean",
     "pretest": "npm run lint",