Add codecov dev dependency

package.json

@@ -77,6 +77,7 @@
     "@babel/preset-react": "^7.0.0",
     "@svgr/rollup": "^4.1.0",
     "babel-eslint": "^9.0.0",
+    "codecov": "3.3.0",
     "cpx": "1.5.0",
     "cross-env": "^5.2.0",
     "eslint": "5.12.0",