Add coveralls

.travis.yml

@@ -39,3 +39,6 @@ script:
         wct --env saucelabs-cron;
       fi;
     fi
+
+after_success:
+  - cat ${TRAVIS_BUILD_DIR}/coverage/lcov.info | coveralls

README.md

@@ -1,7 +1,8 @@
 [![Published on webcomponents.org](https://img.shields.io/badge/webcomponents.org-published-blue.svg)](https://www.webcomponents.org/element/vaadin/vaadin-element)
 [![Build Status](https://travis-ci.org/vaadin/vaadin-element.svg?branch=master)](https://travis-ci.org/vaadin/vaadin-element)
+[![Coverage Status](https://coveralls.io/repos/github/vaadin/vaadin-element/badge.svg?branch=master)](https://coveralls.io/github/vaadin/vaadin-element?branch=master)
 [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/vaadin/web-components?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
-  
+
  [![Published on Vaadin  Directory](https://img.shields.io/badge/Vaadin%20Directory-published-00b4f0.svg)](https://vaadin.com/directory/component/vaadinvaadin-element)
 [![Stars on vaadin.com/directory](https://img.shields.io/vaadin-directory/star/vaadin-element-directory-urlidentifier.svg)](https://vaadin.com/directory/component/vaadinvaadin-element)
 

package.json

@@ -23,6 +23,7 @@
   },
   "devDependencies": {
     "bower": "latest",
+    "coveralls": "^3.0.1",
     "eslint": "^4.13.0",
     "eslint-config-vaadin": "latest",
     "eslint-plugin-html": "^4.0.0",