chore(package): add funding

[curbengh]

What does it do?

Show funding info in npm fund hexo. npm fund is introduced in npm 6.13.

Ref: npm/cli#273, RFC

How to test

git clone -b npm-fund https://github.com/curbengh/hexo.git
cd hexo
npm install
npm test

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[coveralls]

Coverage remained the same at 97.144% when pulling 631b22a on curbengh:npm-fund into 6fa7ada on hexojs:master.

[coveralls]

Coverage remained the same at 97.144% when pulling 631b22a on curbengh:npm-fund into 6fa7ada on hexojs:master.