Update version script to work with Mac (#31)

* Update version script to work with Mac

* Fix version script to add prefix "v"

* Add CHANGELOG.md to git stage after updating version

package.json

@@ -42,7 +42,7 @@
     "preversion": "npm-run-all --npm-path yarn --parallel format:check lint:all test:coverage",
     "test": "cross-env NODE_ENV=test mocha",
     "test:coverage": "cross-env NODE_ENV=test nyc mocha",
-    "version": "bash version.sh",
+    "version": "node version.js && git add -A CHANGELOG.md",
     "watch": "babel src --out-dir lib -w"
   },
   "devDependencies": {

version.js

@@ -0,0 +1,14 @@
+const fs = require('fs')
+const path = require('path')
+
+const unreleased = '## [Unreleased]'
+const [date] = new Date().toISOString().split('T')
+const version = `## v${process.env.npm_package_version} - ${date}`
+
+const changelog = path.resolve(__dirname, 'CHANGELOG.md')
+const content = fs.readFileSync(changelog, 'utf8')
+
+fs.writeFileSync(
+  changelog,
+  content.replace(unreleased, `${unreleased}\n\n${version}`)
+)