changes name of yarn cov output file to the standard name used in coverage gutter

package.json

@@ -17,7 +17,7 @@
     "migrate:dev": "ZESJE_SETTINGS=$(pwd)/zesje.dev.cfg FLASK_APP=zesje/__init__.py flask db upgrade",
     "migrate": "FLASK_APP=zesje/__init__.py flask db upgrade",
     "prepare-migration": "ZESJE_SETTINGS=$(pwd)/zesje.dev.cfg FLASK_APP=zesje/__init__.py flask db migrate",
-    "cov": "python -m pytest --cov=zesje --cov-report=xml:coverage.xml tests/"
+    "cov": "python -m pytest --cov=zesje --cov-report=xml:cov.xml tests/"
   },
   "standard": {
     "parser": "babel-eslint",