Add EOL when overwriting package.json

[nexdrew]

Otherwise changes to package.json b/w releases can end up flip-flopping the last line since editors like Atom will automatically add it but standard-version strips it off - just becomes annoying, unnecessary changes in history and in PRs.

I think we just need to change this line:

fs.writeFileSync(pkgPath, JSON.stringify(pkg, null, 2), 'utf-8')

to something like this:

fs.writeFileSync(pkgPath, JSON.stringify(pkg, null, 2) + require('os').EOL, 'utf-8')

[stevemao]

Didn't know about require('os').EOL, I used to just use \n :D