Add --coverage flag to test script

Prior to this change, the coverage was not being generated during CI test phase and, therefore, not being published on Code Climate

package.json

@@ -20,7 +20,7 @@
   "scripts": {
     "validate": "tsc --noEmit",
     "lint": "eslint 'src/**/*.ts' 'test/**/*.ts'",
-    "test": "jest -c jest.config.js",
+    "test": "jest -c jest.config.js --coverage",
     "rollup": "rollup -c rollup.config.js",
     "rollup-min": "rollup -c rollup.config.js --environment minify"
   },