Add code coverage

.gitignore

@@ -1,2 +1,3 @@
 node_modules
 dist
+coverage

.travis.yml

@@ -1,3 +1,3 @@
 language: node_js
 node_js: node
-script: npm run lint && npm test
+script: npm run lint && npm run coverage

package.json

@@ -11,7 +11,9 @@
     "babel-plugin-add-module-exports": "^0.1.2",
     "babel-preset-es2015": "^6.6.0",
     "chai": "^3.5.0",
+    "codecov": "^1.0.1",
     "eslint": "^2.8.0",
+    "istanbul": "^0.4.3",
     "mocha": "^2.4.5",
     "pre-commit": "^1.1.2"
   },
@@ -21,6 +23,7 @@
     "pretest": "npm run build",
     "test": "mocha test",
     "lint": "eslint src",
+    "coverage": "istanbul cover _mocha -- -R spec && codecov",
     "prepublish": "npm run build"
   },
   "pre-commit": [