ci: add cobertura coverage report

package.json

@@ -17,7 +17,7 @@
     "prepublishOnly": "npm ci && npm run build",
     "preversion": "npm run prepublishOnly",
     "push": "git push && git push origin \"v$npm_package_version\"",
-    "test": "nyc mocha --require source-map-support/register --require ts-node/register 'test/**/*.spec.ts'",
+    "test": "nyc mocha 'test/**/*.spec.ts'",
     "lint": "eslint --ext .ts src/"
   },
   "author": "Karl-Philipp Wulfert <krlwlfrt@gmail.com>",
@@ -83,6 +83,7 @@
     "lines": 95,
     "per-file": true,
     "reporter": [
+      "cobertura",
       "html",
       "text-summary"
     ],