nyc cleanup re-added

Author: RobinBuschmann

package.json

@@ -14,7 +14,8 @@
     "cover-v4": "npm run prepare-test-v4 && nyc --exclude lib/models/v3/**/*.js mocha",
     "exec-tests": "mocha test/specs/",
     "test": "npm run test-v4 && npm run test-v3",
-    "cover": "npm run cover-v4 && npm run cover-v3",
+    "clean-nyc": "rimraf .nyc_output && rimraf coverage && npm install",
+    "cover": "npm run clean-nyc && npm run cover-v4 && npm run clean-nyc && npm run cover-v3",
     "lint": "tslint ."
   },
   "repository": {