chore: adding codecov configuration

Author: developher-net

.travis.yml

@@ -1,6 +1,11 @@
 language: node_js
 node_js:
   - "stable"
+install:
+  - npm install -g codecov istanbul
+script:
+  - istanbul cover ./node_modules/mocha/bin/_mocha --reporter lcovonly -- -R spec
+  - codecovn
 jobs:
   include:
     # Define the release stage that runs semantic-release