chore(deps): update dependency nyc to v14 (#581)

Author: renovate[bot]

handwritten/spanner/package.json

@@ -109,7 +109,7 @@
     "mocha": "^6.0.0",
     "mv": "^2.1.1",
     "npc": "0.0.1",
-    "nyc": "^13.0.0",
+    "nyc": "^14.0.0",
     "p-limit": "^2.2.0",
     "power-assert": "^1.6.0",
     "prettier": "^1.13.7",