chore: fix npm script for send coverage report (#55)

Author: yoshinorin

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "eslint": "eslint .",
     "test": "mocha test/index.js",
-    "test-cov": "nyc npm run test"
+    "test-cov": "nyc --reporter=lcovonly npm run test"
   },
   "directories": {
     "lib": "./lib"