feat: add npm run release script to ease versionning (#64)

Using release-it, alternative to semantic-release.

`npm run release` will:
- bump the version number in package.json
- update the changelog, based on conventional commits
- create a release on github

This should make my life easier!

Also, this PR updates node.js from version 8 to version 10.

.env.sh.example

@@ -0,0 +1,7 @@
+# Todo:
+# 1. generate a token with 'repo' scope from https://github.com/settings/tokens
+# 2. paste it between the quotes below
+# 3. save this file as `.env.sh` and keep it to yourself
+# 4. run `$ chmod +x .env.sh`
+# 5. run `$ npm run release` to release a new version on github
+GITHUB_TOKEN=""

.gitignore

@@ -26,3 +26,4 @@ plato/
 /public/scripts/exam-data.js
 /.firebaserc
 .firebase
+.env.sh

.nvmrc

@@ -1 +1 @@
-v8.16.2
+v10.16.3