Add nyc and coveralls (#115)

Author: Lars-Magnus Skog

.gitignore

@@ -1,2 +1,3 @@
 node_modules
 yarn.lock
+.nyc_output/

.npmignore

@@ -0,0 +1,2 @@
+.nyc_output/
+.github/ISSUE_TEMPLATE.md

.travis.yml

@@ -10,3 +10,5 @@ node_js:
   - 6
   - 8
   - 10
+
+after_success: npm run coverage

README.md

@@ -10,6 +10,7 @@
 [![Travis](https://img.shields.io/travis/Level/level.svg?label=travis)](http://travis-ci.org/Level/level)
 [![AppVeyor](https://img.shields.io/appveyor/ci/Level/level.svg?label=appveyor)](https://ci.appveyor.com/project/Level/level)
 [![dependencies](https://david-dm.org/Level/level.svg)](https://david-dm.org/level/level)
+[![Coverage Status](https://coveralls.io/repos/github/Level/level/badge.svg)](https://coveralls.io/github/Level/level)
 [![JavaScript Style Guide](https://img.shields.io/badge/code_style-standard-brightgreen.svg)](https://standardjs.com)
 [![npm](https://img.shields.io/npm/dm/level.svg)](https://www.npmjs.com/package/level)
 

package.json

@@ -23,12 +23,15 @@
     "opencollective-postinstall": "^2.0.0"
   },
   "devDependencies": {
+    "coveralls": "^3.0.2",
+    "nyc": "^12.0.2",
     "standard": "^11.0.0",
     "tape": "^4.2.2",
     "verify-travis-appveyor": "^3.0.0"
   },
   "scripts": {
-    "test": "standard && node test.js && verify-travis-appveyor",
+    "test": "standard && nyc node test.js && verify-travis-appveyor",
+    "coverage": "nyc report --reporter=text-lcov | coveralls",
     "postinstall": "opencollective-postinstall || exit 0"
   },
   "engines": {