chore(deps): update dependency nyc to v13 (#90)

Author: renovate[bot]

packages/google-cloud-dns/package.json

@@ -78,7 +78,7 @@
     "intelli-espower-loader": "^1.0.1",
     "jsdoc": "^3.5.5",
     "mocha": "^5.2.0",
-    "nyc": "^12.0.2",
+    "nyc": "^13.0.0",
     "power-assert": "^1.5.0",
     "prettier": "^1.13.5",
     "proxyquire": "^2.0.1",

packages/google-cloud-dns/samples/package.json

@@ -20,7 +20,7 @@
   "devDependencies": {
     "@google-cloud/nodejs-repo-tools": "^2.3.0",
     "ava": "^0.25.0",
-    "nyc": "^12.0.2",
+    "nyc": "^13.0.0",
     "proxyquire": "^2.0.1",
     "sinon": "^6.0.1",
     "uuid": "^3.3.0"