ci: add test coverage reporting and tests on node 10 and 12 (#66)

adds code coverage reporting using `nyc`, uses `codecov` to track coverage

* build: update dependencies to remove vulnerabilities

* docs: add coverage badge to readme

.gitignore

@@ -7,3 +7,5 @@ dist
 .validateignore
 .idea/
 bin/
+.nyc_output/
+coverage/

.travis.yml

@@ -1,11 +1,15 @@
 language: node_js
 node_js:
-- '8'
+- 8
+- 10
+- 12
 script:
 - npm run test-travis
+after_success:
+- npm run report-coverage
 deploy:
 - provider: script
   skip_cleanup: true
   script: npx semantic-release
   on:
-    branch: master
+    node: 12

README.md

@@ -1,5 +1,6 @@
 [![Build Status](https://travis-ci.com/IBM/openapi-validator.svg?branch=master)](https://travis-ci.com/IBM/openapi-validator)
 [![npm-version](https://img.shields.io/npm/v/ibm-openapi-validator.svg)](https://www.npmjs.com/package/ibm-openapi-validator)
+[![codecov](https://codecov.io/gh/ibm/openapi-validator/branch/master/graph/badge.svg)](https://codecov.io/gh/ibm/openapi-validator)
 [![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg)](https://github.com/semantic-release/semantic-release)
 [![Commitizen friendly](https://img.shields.io/badge/commitizen-friendly-brightgreen.svg)](http://commitizen.github.io/cz-cli/)
 [![CLA assistant](https://cla-assistant.io/readme/badge/ibm/openapi-validator)](https://cla-assistant.io/ibm/openapi-validator)