Add Coveralls to package.json [1/2] (#21017)

Summary:
Adds a new step to the test suite. Test coverage is now collected and sent to Coveralls.

Initial configuration is limited to the Libraries/ and local-cli/ directories. Please let me know if additional directories should be considered.

I have enabled this repo on the coveralls service. The coveralls token has been added to React Native's Circle CI environment variables.

- Track coverage on PRs, and fail PRs that lower the coverage %
- Increase coverage :)

[INTERNAL] [ENHANCEMENT] [.circleci/config.yml] - Start tracking code coverage (JS)

Pull Request resolved: https://github.com/facebook/react-native/pull/21017

Differential Revision: D9724396

Pulled By: hramos

fbshipit-source-id: 61da4478877805f9a9a3c9670b54ddc4e40e958b

package.json

@@ -88,7 +88,17 @@
       "denodeify",
       "fbjs"
     ],
-    "testEnvironment": "node"
+    "testEnvironment": "node",
+    "collectCoverageFrom": [
+      "Libraries/**/*.js",
+      "local-cli/**/*.js"
+    ],
+    "coveragePathIgnorePatterns": [
+      "/__tests__/",
+      "/vendor/",
+      "<rootDir>/Libraries/react-native/",
+      "<rootDir>/local-cli/templates/"
+    ]
   },
   "main": "Libraries/react-native/react-native-implementation.js",
   "files": [
@@ -212,6 +222,7 @@
     "babel-eslint": "9.0.0",
     "babel-generator": "^6.26.0",
     "detox": "9.0.4",
+    "coveralls": "^3.0.2",
     "eslint": "5.1.0",
     "eslint-config-fb-strict": "22.1.0",
     "eslint-config-fbjs": "2.0.1",